update: First implementation of Karma module.

*  Added karma.py with implementation of Karma that gives/removes virtual karma points to/from users.
*  <user>++ increases karma of user by 1 for every 2 pluses.
*  <user>-- decreases karma of user by 1 for every 2 minuses.
*  !karma <user> shows karma for <user>.

Signed-off-by: Jakub Novak <jakub.novak@gmail.com>

update: Removed unnecessary imports.

Signed-off-by: Jakub Novak <jakub.novak@gmail.com>

update: Added description of !karma command.

Signed-off-by: Jakub Novak <jakub.novak@gmail.com>

karma: Fixed grammar.

* Fixed typo in !karma command description.
* Changed !karma output format.

Signed-off-by: Jakub Novak <jakub.novak@gmail.com>