Allow location.add to have dLocation input

Example of usage:
- DoSomethingAt
<player.location.add[<player.location.direction.vector>]>

also, fix some tag meta.
add location.sub,.mul,.div, fix .direction.vector

This adds <location.div> (Divide the location) <location.mul> (Multiply
the location) and <location.sub> (Subtract from the location) to go
along with the existing <location.add>
It also fixes the math in <location.direction.vector>
Example usage:
- explode
<player.location.add[0,1.5,0].add[<player.location.direction.vector.mul[6]>]>
The above will create an explosion 6 blocks directly in front of where
the player is pointing.
Merge pull request #510 from mcmonkey4eva/master

better dLocation math