Initial, incomplete support for static mustaches

Ref #493 for discussion.

This is support for parsing static mustaches, normal mustaches except with `[[ ]]` as the delimiters instead of `{{ }}` (including triples, config options, and everything else normal mustaches support).

Static mustaches will resolve once and then never again, so they are effectively "compile-time" constants on the initial data.

This changeset only adds the parsing and removing the viewmodel registration from Mustache.resolve, Evaluators and References will still work as usual. Waiting on #816 for the rest.

(No conflicts I can see, I don't know why Github can't auto-merge. No Travis for you! Local grunt build passes just fine.)
Ah, gotcha. The template can change them on-the-fly `[[={{`, etc.