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>
Could you please add a simple description of what this function does in its docstring? I haven't enforced this in the past but it would be nice to have and an easy way of preparing for a well defined help command.

See for example https://github.com/mrshu/brutal-plugins/blob/master/basic.py#L13