Mac build, update and OST

Along with the Mac build we've added a soundtrack and some new game features to PC and Mac:

• 2 new enemies and updated progression.

• Fov slider and vsync options.

• HRTF processing for virtual surround sound when using headphones.

The new version of the game uses a new leaderboard. If you want to watch old replays or play the old version, it's still available by opting in to the "2015" beta in Steam.