Fix #242: Refactor Timber::load_template to use filter 'template_include'.

* Timber::load_template now uses the 'template_include' filter rather than do_action('template_redirect').
* See http://codex.wordpress.org/Plugin_API/Action_Reference/template_redirect
Merge branch '242_load_template' of github.com:cambell-prince/timber into cambell-prince-242_load_template

* '242_load_template' of github.com:cambell-prince/timber:
  Fix #242: Refactor Timber::load_template to use filter 'template_include'.
added tests for routing