Add tilemap with metadata

[trex]

This change adds a Tiled built tilemap with metadata for wall collision and player start locations.

Collidable tile layer is default, whereas a non-collidable tile layers are specified using nocollide=true as a custom property on the Tiled layer.

Player starting coordinates are identified by the type player_start on the Tiled object. Unique player coordinates are created for all 4 players and are distinguished by the object name, names include start_yellow, start_magenta, start_cyan, and start_red.

[trex]

@matthewaltman this is not ready for merge yet, but putting it up so that you can pull down and run.

The tileset I am using is made of 32x32 tiles. The player is currently 64x64. Should we resize the player, or the tileset/tilemap?

Prior to merging, I would like to add documentation on designing tilemaps for the project, and possibly shore up the sizing of sprites and tiles, and fit the gameboard to screen.

[matthewaltman]

@trex we can resize the player down in game. I made the player larger so when it is resized after powerup it's not too blurry.