Escape dev commands for chatting.

Allow chatting command strings if prefixed with "//" instead of executing (with a prefix of "/").

> Newbie01: Hey Phrohdoh, how did you give yourself cash?
> Phrohdoh: /givecash

We could either do this or players can prefix their message with a space (as is possible already).
Except I want to output `/foo` not `//foo`.