Improve function signature handling for templates

We pass the 'outline' option through to the filter so that we don't get
the function description in the rendered text and then we can rely on
the argument parsing to ignore the 'template <typename T>' section and
focus on the arguments.
Merge branch 'templates'
Reorganise index page toctrees

Attempt to make it a little more approachable for new people. It had
become quite a mix of links some of which were useful, others of which
weren't really.
Merge branch 'docs'