Cross-references in generated ddoc

[Ary Manzana]

Hi all,

I just submitted a pull request that makes ddoc generate 
cross-references... even for templates!

https://github.com/D-Programming-Language/dmd/pull/865

It would be awesome if you can try it with your projects, see if it's 
working properly and doesn't choke. I tried it with phobos and it worked 
fine.

Also, if someone has ideas about how to solve the issues I describe, 
they are more than welcome.