Support channel passwords

[jkramer]

Currently only server passwords are supported, but channels can have their own password each which has to be sent along with the /join command. It would be nice to make the channel list in the constructor a hash ("#channel" => "channelpw").

[zoffixznet]

Done. Channels can now be specified either as Str or as a Pair where the key is the channel and value is the password for it:

:channels('#perl6bot', '#zofbot', '#myown' => 's3cret')