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.
I'd like to point out that either way this change should never be part of this pull request. If code is not used it should be removed in a separate pull request.