Made an error message in loadPackages clearer

It's clearer what a package main file should return.
Cleaned up cloud.lua
Made the controllable box push the other box in the test world

I found that if two objects can collide with each other, they will push each other.
Turned on the console

...so I can see debug messages on my Windows computer.
Added math.range and added to math.sign

Now math.sign returns 0 when given 0, just in case.
Implemented a basic walk system for the pony entity
Made overwriting a HC shape field a fatal error

I accidently overwrote shape.move and didn't realise until I decided to
look at the console. The small netbook screen didn't help.

If this error is triggered, the thing that caused it is probably
an accidental overwrite anyway and should be fixed.
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?
Moved world.lua to lib/self

Cleans things up a bit.
Merge branch 'master' into dev

Made a silly mistake and commited a change to the wrong branch.