Moved all test items to z level 0. (floors have a height of 0, so items at the same z level as them will still be on top of them)
Added a test to verify that an object can fall of the map. Test fails because gravity is not implemented yet.
Added up and down heading constants.
Created a gravity function that causes objects to fall after moving unless they collide with a floor or fall of the map. (z level -5) Modified checkForCollision to be callable from both map.move and gravity without the two functions corrupting each other's values.
Created a test that verifies that a robot that drives off a platform will land on a floor below.
Revert "Moved all test items to z level 0. (floors have a height of 0, so items at the same z level as them will still be on top of them)"

This reverts commit 3cdf3910c51e53a286cdbe11f1ffc14b3c61ff6c.
Moved all floors to z level 1. (0 is reserved for divots in the floor)
Item falls of the map when it falls below z level 0.
Merge branch 'master' into gravity

Conflicts:
	domain/Common/heading.js
Revert "Item falls of the map when it falls below z level 0."

This reverts commit 3e7515a7b8cc30c1186721daca6575d3e59de295.
Moved the map bottom into a separate constant on the map for clarity. Also, items fall off at < -5 instead of at -5.
Fixed assertion errors.
Moved the floor to z level 0.
Merge pull request #11 from SamGraber/gravity

Gravity