Takes out documentation for `Merit::Badge.last_granted`.

It should live in a wiki page, outside of merit's repository. See:
https://github.com/tute/merit/issues/111#issuecomment-34876788
https://github.com/tute/merit/issues/138#issuecomment-35232823
Adds deprecation warnings

`Merit::Badge.last_granted` and `Merit::Score.top_scored`
are deprecated.

Please refer to:
https://github.com/tute/merit/wiki/How-to-show-last-granted-badges
https://github.com/tute/merit/wiki/How-to-show-a-points-leaderboard
Deprecates `add_points` `log` parameter.

Judge notifies Observers of reputation changes, and logs an according
message. Data model turns `log` string unnecessary.
Releasing version 1.9.0