Fixed /topic handler
Problem:
/topic This is a test # Would change the topic of channel "This"
    to "is", and ignore the rest
/topic #Channel This is a test # Would change the topic of channel
    "#Channel" to "This" and ignore the rest
Resolution:
If args[0] starts with # or &, a channel has been provided. Set the
    channel's name to args.shift(), and the topic to args.join(' ')
If args[0] does not start with # or &, set the active channel's
    topic to args.join(' ')
Fixing comparison and adding comments, as per #194
Merge pull request #194 from SpenserJ/fix_topic_command_handler

Fixed /topic handler