Add basic colour reformatter

The BaseReformatter just strips colours.
Use BaseReformatter in the pretty printer
Add ANSI formatter
Add ANSI reverse support and fix bell
Bugfixes and XTerm support
Add xterm 256 colour reformatter
Select the best formatter possible
Update TODO
Fix a thinko
Change default nick to meow
Fall back to BaseReformatter (colour stripping) when TERM is unset
XTerm256ColourReformatter → XTerm256Reformatter
Merge branch 'master' into irc-formatting