Fixed bugs with message lengths and Spotify URIs

Maximum input lengths for the user are now determined based on the fixed
length limit from the RFCs and the length of an empty PRIVMSG message
that would be received by another client.

Also fixed Spotify URIs not being shelled properly when private browsing
mode is enabled.
Fixed a race issue with auto commands

Fixed an issue in which auto commands would be executed prior to the
user host mask being retrieved, resulting in runtime errors if channels
are joined upon connection.
Merge pull request #19 from rastating/bug/maximum-message-length

Bug/maximum message length