Moved PM commands to command methods.

Slight rewrite/streamlining in the way PM commands are defined. This makes the
processPM() method cleaner and should improve code readability.
Streamlined in-channel commands.

Repeated the procedure with PM commands on in-channel commands.
Completed streamlining of command methods.

Leaves only a few helper methods.
Replaced "msg" alias and removed "echo" alias.

Also renamed say() to msg().