Provide specific help when user gives a partial command

[menegazzo]

Considering Bender knows to respond foo (.+) regular expression but user has entered only foo. Instead of returning Command not recognized it will be better something like

Missing regex ("foo (.+)")

or

Did you mean "foo (.+)"?

Both responses will guide user to the correct usage of commands but with slight differences: the first option probably requires modifications at respond hook and message should be created in each command; the second option can be done at Bender with difflib.SequenceMatcher.