Comparison operations

Comparing two quaternions can be done component-wise. Two quaternions can represent the same rotation even if they are not identical on a component level. This happens because a quaternion and its inverse rotate to the same spot but they take different routes:

1. Overload the == and != operators in quat.cpp. Add the declaration for these functions to quat.h:

   bool operator==(const quat& left, const quat& right) {
       return (fabsf(left.x - right.x) <= QUAT_EPSILON &&
               fabsf(left.y - right.y) <= QUAT_EPSILON &&
               fabsf(left.z - right.z) <= QUAT_EPSILON &&
               fabsf(left.w - right.w) <= QUAT_EPSILON);
   }
   bool operator!=(const quat& a, const quat& b) {
       return !...