Users ANSI <%code%> shenanigans possible

[DavidRieman]

(Splitting issue from #107.)

Currently a user can type things like say Haha<%up%> GHOST in their communications to have people get "cursor up" commands injected into their output. As-is, this would wreak havoc as clients which support cursor movements (like zMud) will honor the cursor movement command. Basically, this is a class of escape code we should not give a means to replicate through characters which pass user input sanitization processes. The left/right/up/down cursor movement cases are being removed immediately from AnsiHandler but we need to carefully consider the rest of the cases. Like cls is surely problematic, and possibly hidden could find malicious use, etc.