Prevent API crash by sanitizing user input strings

[jrizzle4shizzle]

If a user includes invalid Roll20 API markup in their player or character name, the TurnMarker crashes. By sanitizing the names, we prevent ignorant or malicious players from crashing the API.

[shdwjk]

Sorry, I just noticed this. I'll take a look and see about integrating your suggestions. I actually do all my development in a different repo, so merging directly here isn't part of my process, but I appreciate you taking the time to send this issue to me, complete with a possible solution!