Update YUI Handlebars to use v2.0.0

This passes unit tests for:
- ie 6, 7, 8, 9, 10 (vms)
- ie 11
- safari 6.0.5
- firefox 32.0.2
- chrome 37.0.2 ....
- ios 7.1.2
- android 2.x.x (vm)
- android 4.x.x (vm)

Its also been tested manually in ie 6, 7, 8 with basic examples.

A unit test had to be updated to reflect that a value of `false` return "false" instead of "".  (https://github.com/wycats/handlebars.js/issues/827)

I didn't see anyting in the release notes for v2.0.0 that should cause any issues but it wouldn't hurt for someone to look over them as well.
https://github.com/wycats/handlebars.js/blob/master/release-notes.md