Update Handlebars to v1.0.10

This updates Handlebars to the latest published [to npm] version: v1.0.10.

This version fixes a regression in 1.0.0-rc.3 which caused nested block helpers to not work correctly. The importing script and YUI module wrappers have been updated to work with the recent changes in how Handlebars' code is organized.

**Note:** `Handlebars.VERSION` will still report as: `"1.0.0-rc.3"`, and the following issue has been filed: https://github.com/wycats/handlebars.js/issues/471