The sng tool by Eric S Raymond is a compiler, which can translate between SNG and PNG.
SNG (https://sourceforge.net/projects/sng/) is a specialized markup language for expressing the contents of a PNG (Portable Network Graphics) in an editable, all-text form.
A patch for MinGW is available (https://sourceforge.net/tracker/index.php?func=detail&aid=3031943&group_id=1012&atid=301012).
With this patch, sng builds and works fine on Windows.