Separating functionality into multiple files.

Attempting to modularize code a bit,

New files:
- player.{cpp,h} for all things player logic (events, update, rendering)
- world.{cpp,h} for general world things (currently just a bloated background
  renderer
- image.{cpp,h} for general contact with SDL imaging stuff

Modifications:
- .gitignore for ignoring the .o files that are now generating when making
- Makefile for compiling the multiple files and link them together
- main.cpp for tearing out main.cpp functionality into new files for modularity