Split Handlebars into its own language

[sprintr]

Now that we have enabled CodeMirror's simple-mode addon in the core, we should split handlebars mode, which uses simple-mode addon, into its own language.

[marcelgerber]

This will give you a raw Handlebars mode without HTML syntax highlighting.

This is how CodeMirror did it:

      CodeMirror.defineMode("htmlhandlebars", function(config) {
        return CodeMirror.multiplexingMode(
          CodeMirror.getMode(config, "text/html"),
          {open: "{{", close: "}}",
           mode: CodeMirror.getMode(config, "handlebars"),
           parseDelimiters: true});
      });

[sprintr]

@marcelgerber Should be fine now.

[marcelgerber]

Looks good to me.

The brackets.js change is a hack, but unfortunately, there's no way 'round this right now.

[TomMalbran]

Why can't we load the mode in the extension? or do a trick like the one used for rpm: #11314?

[sprintr]

@marcelgerber What do you think about loading mode in the extension itself like in #11314 ?

[marcelgerber]

If that works, it's a whole lot cleaner.

[sprintr]

@marcelgerber Yeah, it works. I'll rebase and push.

[sprintr]

Travis CI build has passed. @marcelgerber Can you have a look at it

[marcelgerber]

This is all good & ready to go from my side.

@ryanstewart Do we want this in 1.4 or should we wait for 1.5?

[abose]

Merging.
Thanks @sprintr