Handlebars helpers

[xxgreg]

Add a simple version of helpers as implemented in handlebars.js.

http://handlebarsjs.com/

var t = new Template(
                     '{{ uppercase foo }}',
                     helpers: {'uppercase': (ctx) => ctx.arguments[0].toUppercase()});

 t.render({'foo': 'bar'}); // outputs 'BAR'

These can also be used with sections.

Initial hacky implementation here:

https://github.com/xxgreg/mustache/tree/handlebars-helpers

[MikeMitterer]

👍

[xxgreg]

I'm unfortunately busy with other things at the moment. But I recently rewrote the parser to make it easier to implement helpers. Have a crack at this if you are interested - I'm happy to help with reviews.