Add support for Publishers schema elements

Now that the Publishers schema is an official Committee Specification, please add support for the following new elements:
speaker
Designates a person who is giving a speech or lecture.

line
A line of dialogue or other form of communication.

linegroup
A grouping of lines in dialogue or other form of communication.

poetry
A container for poetry.

dialogue
A container for speeches and other forms of communication involving dialogue.

drama
A container for plays and other forms of dramatic presentation.

As well as support for Dublin Core metadata:
The following Dublin Core elements from the http://purl.org/dc/terms/ namespace have been defined and included in the Publishers schema:

title
A name given to the resource.

creator
An entity primarily responsible for making the resource. Examples of a Creator include a person, an organization, or a service. Typically, the name of a Creator should be used to indicate the entity.

subject
The topic of the resource. Typically, the subject will be represented using keywords, key phrases, or classification codes. Recommended best practice is to use a controlled vocabulary. To describe the spatial or temporal topic of the resource, use the Coverage element.

description
An account of the resource. Description may include but is not limited to: an abstract, a table of contents, a graphical representation, or a free-text account of the resource.

publisher
An entity responsible for making the resource available. Examples of a Publisher include a person, an organization, or a service. Typically, the name of a Publisher should be used to indicate the entity.

contributor
An entity responsible for making contributions to the resource. Examples of a Contributor include a person, an organization, or a service. Typically, the name of a Contributor should be used to indicate the entity.

date
A point or period of time associated with an event in the lifecycle of the resource. Date may be used to express temporal information at any level of granularity. Recommended best practice is to use an encoding scheme, such as the W3CDTF profile of ISO 8601 [W3CDTF].

type
The nature or genre of the resource. Recommended best practice is to use a controlled vocabulary such as the DCMI Type Vocabulary [DCMITYPE]. To describe the file format, physical medium, or dimensions of the resource, use the Format element.

format
The file format, physical medium, or dimensions of the resource. Examples of dimensions include size and duration. Recommended best practice is to use a controlled vocabulary such as the list of Internet Media Types [MIME].

identifier
An unambiguous reference to the resource within a given context. Recommended best practice is to identify the resource by means of a string conforming to a formal identification system.

source
A related resource from which the described resource is derived. The described resource may be derived from the related resource in whole or in part. Recommended best practice is to identify the related resource by means of a string conforming to a formal identification system.

language
A language of the resource. Recommended best practice is to use a controlled vocabulary such as RFC 4646 [RFC4646].

relation
A related resource. Recommended best practice is to identify the related resource by means of a string conforming to a formal identification system.

coverage
The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant. Spatial topic and spatial applicability may be a named place or a location specified by its geographic coordinates. Temporal topic may be a named period, date, or date range. A jurisdiction may be a named administrative entity or a geographic place to which the resource applies. Recommended best practice is to use a controlled vocabulary such as the Thesaurus of Geographic Names [TGN]. Where appropriate, named places or time periods can be used in preference to numeric identifiers such as sets of coordinates or date ranges.

rights
Information about rights held in and over the resource. Typically, rights information includes a statement about various property rights associated with the resource, including intellectual property rights.

alternative
An alternative name for the resource. The distinction between titles and alternative titles is application-specific.

tableOfContents
A list of subunits of the resource.

abstract
A summary of the resource.

created
Date of creation of the resource.

valid
Date (often a range) of validity of a resource.

available
Date (often a range) that the resource became or will become available.

issued
Date of formal issuance (e.g., publication) of the resource.

modified
Date on which the resource was changed.

dateAccepted
Date of acceptance of the resource. Examples of resources to which a Date Accepted may be relevant are a thesis (accepted by a university department) or an article (accepted by a journal).

dateCopyrighted
Date of copyright.

dateSubmitted
Date of submission of the resource. Examples of resources to which a Date Submitted may be relevant are a thesis (submitted to a university department) or an article (submitted to a journal).

extent
The size or duration of the resource.

medium
The material or physical carrier of the resource.

isVersionOf
A related resource of which the described resource is a version, edition, or adaptation. Changes in version imply substantive changes in content rather than differences in format.

hasVersion
A related resource that is a version, edition, or adaptation of the described resource.

isReplacedBy
A related resource that supplants, displaces, or supersedes the described resource.

replaces
A related resource that is supplanted, displaced, or superseded by the described resource.

isRequiredBy
A related resource that requires the described resource to support its function, delivery, or coherence.

requires
A related resource that is required by the described resource to support its function, delivery, or coherence.

isPartOf
A related resource in which the described resource is physically or logically included.

hasPart
A related resource that is included either physically or logically in the described resource.

isReferencedBy
A related resource that references, cites, or otherwise points to the described resource.

references
A related resource that is referenced, cited, or otherwise pointed to by the described resource.

isFormatOf
A related resource that is substantially the same as the described resource, but in another format.

hasFormat
A related resource that is substantially the same as the pre-existing described resource, but in another format.

conformsTo
An established standard to which the described resource conforms.

spatial
Spatial characteristics of the resource.

temporal
Temporal characteristics of the resource.

audience
A class of entity for whom the resource is intended or useful.

accrualMethod
The method by which items are added to a collection.

accrualPeriodicity
The frequency with which items are added to a collection.

accrualPolicy
The policy governing the addition of items to a collection.

instructionalMethod
A process, used to engender knowledge, attitudes and skills, that the described resource is designed to support. Instructional Method will typically include ways of presenting instructional materials or conducting instructional activities, patterns of learner-to-learner and learner-to-instructor interactions, and mechanisms by which group and individual levels of learning are measured. Instructional methods include all aspects of the instruction and learning processes from planning and implementation through evaluation and feedback.

provenance
A statement of any changes in ownership and custody of the resource since its creation that are significant for its authenticity, integrity, and interpretation. The statement may include a description of any changes successive custodians made to the resource.

rightsHolder
A person or organization owning or managing rights over the resource.

mediator
An entity that mediates access to the resource and for whom the resource is intended or useful. In an educational context, a mediator might be a parent, teacher, teaching assistant, or care-giver.

educationLevel
A class of entity, defined in terms of progression through an educational or training context, for which the described resource is intended.

accessRights
Information about who can access the resource or an indication of its security status. Access Rights may include information regarding access or restrictions based on privacy, security, or other policies.

license
A legal document giving official permission to do something with the resource.

bibliographicCitation
A bibliographic reference for the resource. Recommended practice is to include sufficient bibliographic detail to identify the resource as unambiguously as possible.