ember-template-compiler exports EmberHandlebars

The Emberized variant of Handlebars should be considered one of the exports/outputs of the ember-template-compiler for those who need it in addition to the exported `precompile` function, e.g. Emblem and anyone else who needs access to the modified EmberHandlebars object. 

This was original put forth as https://github.com/emberjs/ember-dev/pull/1 and closed in favor of splitting out Handlebars, which we did already, but I forgot there are properties Emblem needs to read from the EmberHandlebars object, hence this change.