New game mode: handicap

From the mode description: Handicap: Frag everyone to increase your handicap. Handicap corresponds to frag differences between players. Health, armor, damage are reduced by current handicap.

Hence, better players have less health, less armour and cause less damage. E.g. if you are leading with 24 frags and the weakest player has got 21 frags, your handicap is 74. Health/Armour/Damage are scaled by 74/100. It becomes harder to frag weak players and easier for them to frag you. Equal number of frags means same handicap. When 2 players with equal number of frags meet, it feels like playing normal FFA. Think of it as of the handicap in Golf. It enables people with different strength to play together and still have the same fun.

It is tested and fun. "But I'm not good enough. It's no fun for me." was yesterday. This not an excuse anymore for not playing.

Install:
- Attached zip file contains patched files from the justice edition src/ and data/ trees and the corresponding diff.
- Download Sauerbraten Justice Edition.
- Apply the patch OR replace the files in the original src/ and data/ directories by the ones in the zip file, i.e. extract the zip in the sauerbraten directory.
- Compile game.
- Have fun!