Use an enum for ANSI output state

No functional change with regard to the ANSI output state, just making the code easier to read.

Removed the conversion of `[ and \xFA[ to \x1b[ in putmsg(). This unexplained output translation has been supported since at least v2.xx and I have no recollection of exactly why it was added. If I recall correctly, some BBS software at some point in time sent ANSI-encoded messages into message networks by translating the ESC (\x1b) character in the ANSI sequences to either ` or \xFA in the process. This "feature" seems like it would still work, but it's completely undocumented and I have no idea why it was added (and seriously doubt anyone relies on this behavior), so I'm removing it. If anyone misses this feature, I'll happily add it back, but I'm skeptical that'll happen.