Go Template grammar

Derived from GoSublime.
ref #26.

A [conversion](https://atom.io/docs/v0.135.0/converting-a-text-mate-bundle) of [GoSublime-Template.tmLanguage](https://github.com/DisposaBoy/GoSublime/blob/master/syntax/GoSublime-Template.tmLanguage) and in RAW strings based on [a previous commit](https://github.com/DisposaBoy/GoSublime/commit/f2ffba8c07e9fd6039dbfa26bb8f49a3342e09ae) to GoSublime-next.tmLanguage. In the later case, there was also a `#string_placeholder` pattern but that doesn't exist in Atom's cson (compare with the [CSON from converting from GoSublime](https://gist.github.com/nathany/5ca807701fcdf4a09f44)).

It is working, but I'm not yet familiar with TextMate/SublimeText/Atom grammars.

![gotemplate](https://cloud.githubusercontent.com/assets/4566/4514626/cc7b6ef2-4b7f-11e4-8527-4152c9f439a3.png)

![raw-string-template](https://cloud.githubusercontent.com/assets/4566/4514628/cf72db04-4b7f-11e4-8a53-d1e9de171e7e.png)

I just noticed that he has [another grammar](https://github.com/DisposaBoy/GoSublime/blob/master/syntax/GoSublime-HTML.tmLanguage) just to add the .gohtml fileType.