Bump to handlebars-1.0.0-rc.3

Also use cdnjs for source URL because they have up-to-date minified and
non-minified files for various JS projects (the handlebars.js downloads
is 5 months behind)
Merge pull request #1 from wjlroe/handlebars-1.0.0-rc.3

Bump to handlebars-1.0.0-rc.3