Switch to using the skybot engine, which is considerably less shitty than the previous IRC lib
Clean up butt plugin
Improve handling of unbuttable sentences
Add more block words
Raise an exception when something can't be butted
Ensure that if a @hook.singlethread hook throws, we keep running it
Use time-based auto-butting instead of line-based
Add a minimum line count before butting, in addition to the new minimum time delta
Remove a spurious print statement
Fix typo in README url