when nick is already taken, library should attempt to connect with a modified nick

[jfhbrook]

For example, when irssi can't connect as 'jesusabdullah' it tries again with 'jesusabd1llah'.

[edef1c]

I'm not sure we want this builtin. It's an easy thing to mix in, IMHO.

[edef1c]

/cc @mmalecki

[mmalecki]

See #14.