css: renamed m-doxygen.css to m-documentation.css.
And all .m-dox* classes to .m-doc*. It's not Doxygen-specific anymore.
Note this is a breaking change if you are using the Doxygen theme. In
particular:
* all stylesheet references in HTML_EXTRA_STYLESHEETS have to be
updated to reference m-dark+documentation.compiled.css instead of
m-dark+doxygen.compiled.css
* all processing scripts and theme derivations that were depending on
the m-doxygen.css file need to reference m-documentation.css
* all theme modifications need to use the m-doc prefix instead of
m-dox for CSS classes