Add efficiency calculation to game system

[jthingelstad]

Efficiency is calculated as the percent of field kubbs toppled with the first baton. If you throw 5 kubbs and the first baton takes down 3 the efficiency of that turn is 60%. You average the efficiencies of all turns to determine the efficiency of a team for the whole game.

• Document the means of calculating team efficiency
• Add efficiency calculation to scoring system on wiki