Add comment support to json lexer.

[textshell]

Allows to add comments in documentation of json formats. This commit only allows for one line comments, but should be easy to extend to /* ... */ style comments

This allows documentation in a style like this:

{
    "response": {
        "data": [
            // contact objects
        ],
        "limit": 10,
        "page": 1,
        "totalEntries": 15, // Note total entries changed
        "totalPages": 2
    }
}

Split into an basic commit to enable comments in all contexts except in otherwise empty objects and a separate commit to refactor handling of empty objects to be less of a special case and thus also support comments.

[textshell]

Please also see pull request 244 for a pull request that additionally adds ellipsis syntax and is based on this branch.

[jneen]

superseded by #244