Adding new functionality to truncate messages longer than a specified length.

IRC has a maximum message length of ~500 characters (depending up on implementation, and including commands/arguments).  This PR will set up a maximum message length of 400 characters and truncate the sent message body to maximally that length while taking into account the URL/hostname length.

Given that this has a semi-substantial effect on the message, I've taken the liberty of setting up tests for this module and adding one to verify this functionality.