Lots of changes

Deep Caves #1
* Lay groundwork for yOffset in world.render()

Player Overhaul #12
* No longer extends Item
** Remove affectedByGravity references
* Set proper instance variables

Items #12
* Add Item base class
* Add static Items class to define our items
* Add Item list to cells

Frame Overhaul #13
* add setGbColor()
* add putChar()
* sort out width and height a bit better