Handlebars 2.x Update

Updates the library to run with Handlebars 2.x codebase.

These changes made no attempt at backwards compatibility between the versions, but it seems like it would be possible if these are the project requirements.

Tests are passing locally but are pending the release of the beta (and the bower/npm updates tied to that). I'll be releasing the code that is master tomorrow evening or Weds as 2.0.0-beta.1.