Added arguments property to Message, Updated botcommands to use
property.
Extracted Message class out to its own file
Removed Racer.averageRate() and old completionRate command that used it.
Improved Racer.averageTime, Added Racer.medianTime, and updated botcommands to use them
Switched teamTime calculations to use median time instead of average
Added !say and !command for admin use.
Addded !join and !leave commands that can be used by normal users