[Standards] Escape characters in XEP-0393: Message Styling

Hello, first of all, this is my first attempted contribution to an Internet standard, so I do apologize if the form is a bit off. That said, I was implementing a parser for "XEP-0393: Message Styling", and I ran into the issue that not much is defined in the way of escape characters. In Gajim, for instance, the sequence *hello* becomes bold, the sequence \*hello* does not, but the sequence \\*hello* also does not. In many applications, preceding a \ with another \ escapes the latter \, making it so that the escape character itself is escaped, and therefore the * that creates the emphasis span would not be. However, the standard does not mention any rule regarding this (and Gajim does not do what I expect), so it is perhaps a good idea to add a note about this before making it final. Kind regards, Werner