Partials loading through RequireJS

Allows autoloading of partials by recursively using RequireJS

* Absolute partial paths `{{> /path/to/partial}}`
* Relative (to current template) partial paths `{{> ./siblingPartial}}`
* `pathPrefix` for default partial path lookups, e.g. `pathPrefix: 'templates'`
  * `{{> lib/sharedPartial}}` => `templates/lib/sharedPartial.mustache`