Function rotate

rotate(out: mat4, a: ReadonlyMat4, rad: number, axis: ReadonlyVec3): mat4
Rotates a mat4 by the given angle around the given axis
Parameters
- out: mat4
  the receiving matrix
- a: ReadonlyMat4
  the matrix to rotate
- rad: number
  the angle to rotate the matrix by
- axis: ReadonlyVec3
  the axis to rotate around
Returns mat4
out