add loosen_by_vector and tighten_by_vector, which does the spective operation in each dimension, according to the vector passed in

[rezural]

This adds four methods to the bounding_volume trait, and the AABB implementor:

fn loosen_by_vector(&mut self, amount: Vector); fn loosened_by_vector(&self, amount: Vector) -> Self; fn tighten_by_vector(&mut self, amount: Vector); fn tightened_by_vector(&self, amount: Vector) -> Self;

for situations where one only wants to tighten/loosen in a subset of available dimensions.

[rezural]

Disregard this, needs work