Reworded package notes and noted a bug with pushing

The notes on the package system now state that the
system is implemented.

When objects "push" one another, they are being displaced
by the mtv given by HardonCollider as opposed to their
velocity being set. I believe this is allowing objects
to be pushed inside and through other objects, such
as the world boundaries.
Cleaned up world.lua and gave world boundaries their own type
Made preparations for different movement types for ponies

Speeds and accelerations for the movement types were
organised in a table.

This functionality should probably be given its own
entity, ie. moveable? creature?