Alias and variable template support

[melton1968]

I need to document several meta-functions and variables that appear as alias and variable templates:

template<class T>
using Fuzzy = std::integral<T>;

template<class T, class U>
constexpr bool Furry = std::same_v<T,U>;

The current master version of breathe was dropping the template<class T> part of the declaration in each case, so I inserted single lines in visit_variable and visit_declaration to prepend the template prefix back to the declaration right before rendering.

I am unsure if this is the appropriate fix, but I did not detect any changes in the resulting breathe documentation pages (save for the template_type_alias specific test I added).

I would be very happy if this functionality could be integrated into the master branch and eventually a release.

cheers,
mark

[vermeeren]

4.14.0 has been released containing this patch.