Add support for more doxygen directive

[TonyWelte]

This PR adds support for several Doxygen directives:

• the conversion of math formulas from "$formula$" to ":math:formula" to follow the reST format. This enables formulas to be correctly displayed with tools such as Sphinx

[themarpe]

@TonyWelte are deprecation tags also on your TODO? :)
Not sure how those are / should be converted, just wondering

[TonyWelte]

I have added the tags:
\deprecated --> .. deprecated:: (reST expects a version number so the first word is assumed to be the version number)
\since --> .. versionadded::
\todo --> .. todo::
Warning: I haven't been able to test this, I'm suffering from #2

[themarpe]

@TonyWelte

Nice! And these can be written both with \ and @ right?

Check my PR for #2 -> #10 and let me know if it works for you:)

[TonyWelte]

@themarpe Yes, both \ and @ can be used.

Thanks for #10, I was able to test it and fix an issue. It should be done now.