Refactored TimberTemplateLoader to be instantiated with a TimberLoad object
Allow cached $context to be force refreshed
Force refresh Timber::get_context cache in unit tests
Let TimberLoader use the template loader when choosing a template and the constant TimberLoader::AUTOLOAD_TEMPLATE is passed
Added (failing) unit tests for Timber::render and ::compile using both overloading and the TimberLoader::AUTOLOAD_TEMPLATE constant
Make $filename argument for Timber::render and Timber::compile optional through overloading