This allows you to strictly require a number of arguments. The default
behaviour in this case is still `True`, since it would be a breaking
change otherwise and is a sane default. However if someone would want
to set this to `False`, they would receive an exception of type
`TooManyArguments` if too many arguments are passed to a command.
Hopefully this removes the uses of `ctx.message.content == 'stuff'`
inside commands.
This change should make it a bit more intuitive to get the original
exception without having the gotcha of checking ``isinstance`` inside
the error handler.
