Improved collision + further cleanup

2014/04/07
-Worked out how to do collision detection for cubes without testing
collision on themselves
-Added StepAxis() function to Entity to further clean up ApplyVelocity()
code
-Added another enum to Entity called BITSHIFT
-Basically a cop out to get rid of some of the magic numbers related to
bitshifting
-Created function which outputs true when one object is directly above
another for use in jumping
-Moved FillScreenblock() function to Level class
-Realised I had no FlipBuffers() in the main (woops!), so that's been
added
-Formatted all files such that no line is no more than 100 characters
long