partially-working sqlite-based usermasks
WHOWAS command
move ClientLookupSet to its own file
implement WHOWAS with a shared ringbuffer
update ClientLookupSet when username changes
minor cleanup/refactoring
Merge remote-tracking branch 'origin/master' into user-mask

Conflicts:
	irc/reply.go
	irc/server.go
	irc/types.go
mask lists (ban, except, invite)
Merge remote-tracking branch 'origin/master' into user-mask
channel invite mode/list
persist and load channel mask lists
print message when exiting main program
comments and improvements for client set
Merge remote-tracking branch 'origin/master' into user-mask

Conflicts:
	irc/types.go
Merge pull request #16 from jlatt/user-mask

support user mask wildcards through an in-memory sqlite db