Mustache indentation

[devth]

mustache.vim should know how to indent opening and closing mustache tags:

{{#items}}
  {{foo}}
{{/items}

[juvenn]

Currently, the indent part is just borrowed from html indent, and I assumed the plugin is used in html environment only. This kind of indent is a bonus feature, that I may work on it some time later.

Pull requests are very well welcomed, if you can work it out.