feat(game): put friends, group, inventory, skills in Game instead of Character

feat(combat): support self targeted and area skills

Merge pull request #32 from Rutherther/combat

Add combat extension

feat(combat): remove item selector from simple attack technique

fix(combat): null skill after it was used

feat(combat): make target id long

feat(combat): return current target from combat technique

docs(combat): add missing documentation

feat(combat): add simple attack combat technique