#621 Remove support for xhtml

[Lee Worden]

Up-to-date releases of MediaWiki produce HTML5 output only, not HTML 4 or XHTML. In the past we had to mess with XHTML because browsers wouldn't accept MathML in HTML 4, but now we don't. Browsers that do MathML are happy to do it in HTML5 pages, and we support browsers that don't by giving them MathJax with the HTML5 output. So the extra stuff about XHTML is irrelevant, and uses MW globals that no longer exists. Time to remove it.

See also: [#225] .html, .xhtml, .html5

[Lee Worden]

So I'll be removing the $ww variables that control whether to output XHTML, mathjax, etc., and making mandatory the current default behavior of providing MathJax to all clients except when the user has opted for native MathML support and the client supports it.

I'll also be resolving [#225] by tweaking the WW latexml make rules, so that %.latexml.html produces the same output as %.latexml.html5, and adding a %.html : %.tex rule that does the same as those.

[Lee Worden]

And WW will no longer have the "fallback" feature where requesting a %.xhtml file changes it magically to a %.html file if you're in a no-MathML browser.

[Lee Worden]

I'll need to test with and without the MathML preference set.

[Lee Worden]

and remove the backward-compatibility latexml.compat.css file

[Lee Worden]

And remove all references to $wwUseMathJax.

[Lee Worden]

And no longer support "htmldisplay=" in addition to "display=" in WW tags and on the GPF url.

Q: what to replace wwfCanDoMathMLWIthoutXHTML() with?
A: create wwfUseMathJax() function. Get rid of functions: wwfCanDoMathMLWithoutXHTML, wwfCanServeAsXHTML, wfCanServeAsXHTML, wwfUserRequestedMathML, wwfShouldServeAsXHTML, wfShouldServeAsXHTML, WWInterface::okay_to_serve_mathml