quatcompress
Compress a normalized quaternion into 32 bits.
Single C header file with static inline functions.
On random quaternions, mean error is 0.08 degrees and worst-case error is 0.25 degrees.
Always returns a quaternion where the element of largest magnitude is positive.
This saves 1 bit, but it creates the possibility that quaternion elements will
flip signs when the underlying rotation only changes slightly.
Since q and -q represent the same rotation, code that uses quaternions
correctly should be able to handle sign flips without any problem.