Preserve fancyhdr.sty content

[dginev]

We have a stub in place for fancyhdr.sty, which is expedient in discarding the header content. We've had an arXiv author request more complete support, as they had valuable licensing information in the header.

An example article is 2306.06056.

As an example of the stub binding lines:

LaTeXML/lib/LaTeXML/Package/fancyhdr.sty.ltxml

Lines 27 to 29 in dfc3bc9

	DefMacroI('\fancyhead', '[]{}', '');
	DefMacroI('\fancyfoot', '[]{}', '');
	DefMacroI('\fancyhf', '[]{}', '');