Upgrade handlebars-source.

* handlebars-source upgraded to 1.3.0
* Unit test added for some of the 1.3.0 Handlebars functionality ([whitespace control](http://handlebarsjs.com/block_helpers.html#whitespace-control))
* common-js dependency removed due to `Handlebars` being exported globally.
* Cleaned up the README to remove the submodule stuff and renamed header to Test
* `Handlebars::Context::runtime` was removed because it seemed odd to use the pared down `handlebars.runtime` in a server-side environment.
* Version bumped to 0.6.0

Fixes #26