Quaternions to Euler angles conversion

Convert quaternions to Euler angles. Note that the Euler angles are different for different rotation sequence. The Euler angles rotation sequence used in this code is z-y'-x'' (yaw, pitch, roll). The rotation is intrinsic, i.e., rotates along new axes. This definition is widely used by aerospace engineers.

Reference: https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles

Verification: www.andre-gaschler.com/rotationconverter/
Note that quaternions to Euler is not unique but Euler to quaternions is unique. So it is better to get the Euler of a normalized quaternions (such as [ 0.7071068, 0, 0.7071068, 0]) from the function and use the verification tool to convert the Euler to quaternions. The quaternions should match if the rotation sequence is correctly chosen.