Add tests for layouts (these should fail now)
Add support for default layout

- Users can now specify a default layout and layout path to use.
- The render generator function causes partials and layouts to be
  cached. There is probably a better way to do this, but now
  everything is guaranteed to be loaded when a template is
  rendered.
- Update tests
Add support for template specific layouts

- Specify a layout by adding `{{!< layoutName }}` somewhere in
  your template.
- Update README
Tweak readme and increment minor version
Merge pull request #1 from jwilm/layouts

Add layout support