Several new @-codes that can be used to display user's configuration settings

I'll add detailed docs to http://wiki.synchro.net/custom:atcodes soon, but the
list is:

- TERMTYPE
- TERMROWS
- TERMCOLS
- AUTOTERM
- ANSI
- ASCII
- COLOR
- ICE
- RIP
- PETSCII
- SWAPDEL
- UTF8
- MOUSE
- UPAUSE
- SPIN
- PAUSESPIN
- EXPERT
- HOTKEYS
- MSGCLS
- REMSUBS
- FILEDESC
- FILEFLAG
- AUTOHANG
- AUTOLOGON
- QUIET
- ASKNSCAN
- ASKSSCAN
- ANFSCAN
- EDITOR
- SHELL

This should (at least mostly) address the issue #629