Preliminary Minecart physics handling [SEE DESC]

This commit includes physics handling for the following scenarios:

Flat rails in orientations [N, S, W, E]
Ascending/descending rails in orientations [N, S, W, E]

Powered rails are NOT handled (they don't respond to redstone).
Curved rails are NOT handled (I haven't figured out how to do them :P)

Please note that I have not tried to emulate vanilla behaviour because
of a lack of knowledge on velocity unites/C++. We can say it's a feature
or something. :P
Zomb-ee and Skellingtons burning improvements

They don't burn unless they are in direct view of the sun god or are
protected by the sands of the souls of the underworld.