Added ability to have deep partials. Now supports {{>sub-dir/partial}}.

Added ability to have subdirectories of partials.

Now docs can have a tree of:
docs -
- partials
  - exampleA
     - full.mustache
     - markup.mustache
     - style.mustache
  - exampleB
     - full.mustache
     - markup.mustache
     - style.mustache

This promotes a more modular approach to partials and example support files.