fix(rewrite): Handle formatting of json comments when adding new resourc...

...e roots

Add new method addCommaToLine(args) which allows you to find a line in a file
 and add a terminating comment char at a specified offset from that line. Uses
 same methods as in rewrite(args).
This solves the issue where new resource roots required a comma at the beginning of the line which did not look pretty.

Fixes #55 #57

This works great when using a clever editor like sublime, but if you're a poor sole that uses NotePad then there is still an issue with windows carriage returns in rewrite() that I don't have time to get to the bottom now... I think we should just leave it - and maybe even remove all concerns about windows carriage returns. i.e. ignore doing this: ```lines[otherwiseLineIndex] += "\r";``` No harm in having it in there though.