Fix LaTeX/MathJaX formatting in messages

[thundergolfer]

Some papers from Arxiv have LaTeX in their abstracts, which is inconveniently prefixed with something like ///e. All those forward slashes where screwing with my JSON parsing, so I just went in a substituted the LaTeX/MathJaX prefix for something that wouldn't cause trouble (likeMATHJAX).

Before it's sent to the user, I need to replace these substitutions with something that enables LaTeX viewing in Slack. It's not natively supported in the application, but there is something you can do/install to get LaTeX rendering happening. At the least I don't want these MATHJAX prefixes littering the bot's responses.