Dot product
Like with vectors, the dot product measures how similar two quaternions are. The implementation is the same as the vector implementation. Multiply like components and sum the result.
Implement the quaternion dot product function in quat.cpp and add its declaration to quat.h:
float dot(const quat& a, const quat& b) {
    return a.x * b.x + a.y * b.y + a.z * b.z + a.w * b.w;
}
Like vectors, the length of a quaternion is the dot product of the quaternion with itself. In the next section, you will learn how to find the squared length and length of a quaternion.
