Type fix and add setPosition method

[fenomas]

Hi,

Two small changes:

1. Change vec property to explicitly create a gl-vec3, rather than using the passed-in value. This forces all properties to have the same type (i.e. Float32Array) even if user passes in plain arrays
2. adds setPosition( [x,y,z] ) method (and test cases)

The latter is because I keep accidentally trying to move an aabb by updating box.base values.

Cheers!

[fenomas]

Hi... just wondering if you've seen this, or disagree with anything. Cheers!

[fenomas]

Ping!