[Request]Quaternion from between vectors

[mkohlhaas]

Could we have a function that creates a quaternion from two in-between vectors? Essentially the same function as
Quaternion.fromBetweenVectors(u, v) in Quaternion.js.

The operation could also be optimized.

[ebassi]

I was not planning on adding that API, but I would not say no to a pull request…