Support for Handlebars partials

[naganowl]

The plugin assumes all parsed HBS files are templates, but they can be defined as partials to allow for reuse.

For more info, see

• http://handlebarsjs.com/execution.html
• http://mustache.github.io/mustache.5.html#Partials

[jonnywyatt]

See http://stackoverflow.com/questions/12014547/how-do-i-precompile-partials-for-handlebars-js/12148609 for a workaround