Holiday updates and a trailer

Over the holiday season I made a handful of little updates to Retromancer:

• All of the player classes got tweaked a bit -- the cleric got the biggest adjustments with the addition of charged shots
• Most areas have some ambient visual and audio effects now (dust in the crypts, rain in the swamp, etc)
• Packaged up a MacOS version of the game for the first time, and am happy to say it ran pretty well
• Started putting together a Steam page, which should be live soon
• Cut together a gameplay trailer for the Steam page (and anywhere else that needs to see a chunk of gameplay)