more unit tests for the quaternion to 3×3 matrix conversion.

with the unit tests.

Euler angles to a rotation matrix. Also fix quat::rotate() which was not
building the correct quaternion.

mathematical writing, and add static constructors to create quaternions
from a rotation.

code for all matrices.

"shader" source directory since we have "gpu".

the matrix code itself.

to avoid common programming errors.

reuse the linear operations in quaternions. Also mark some constructors
explicit to better spot coding errors.

function use degrees rather than radians.

cross product, normalize, etc.

According to David Turner, “it should be the only thing that NDK users
should be testing again.”

projection matrices.