Twemoji Support, Take 2

Similar to the PR from before ( #505 ), but now Twemoji parsing is optional and it defaults to disabled. I still plan  on adding UA detection for better default handling, but wanted to get _something_ out while I figure out the best way to do so.
Yes, that is also true. If you want to do some cleanup around the code, that would certainly be a well-appreciated pull request as well! It's just hell to test those things