Implemented `ToPrimitive` and `FromPrimitive` for `MouseButton`
Implemented `ToPrimitive` and `FromPrimitive` for `MouseButton`

Closes https://github.com/PistonDevelopers/input/issues/92

axelmagn/piston,mitchmindtree/piston,PistonDevelopers/input,caldwell/piston,bvssvni/piston,PistonDevelopers/piston,KevinFrans3/piston,tempbottle/piston,placrosse/piston,PistonDevelopers/piston,oldmanmike/piston,Potpourri/piston,bvssvni/piston,getynge/piston,bvssvni/input