Optimized quaternion rotation routine

[infusion]

Hello,

I'm the author of Quaternion.js and derived a simpler method to rotate a vector using normalized quaternions, reducing the number of multiplications quite a bit. Since gl-matrix is developed with performance in mind, I think this addition can improve quite a few code bases.

All your unit tests are passing. I removed the performance test link, since jsPerf is offline for quite some time now.

Robert

[gene-ressler]

This looks like an excellent improvement. I wish it would be merged. My only nit is that adding two floats to implement multiplication by two is probably not worthwhile and possibly slower, since the upshot is a simple increment of the exponent. At any rate, JIT compilation will do the right thing if the code ends up in a critical place.

[toji]

Thank you for the contribution, and sorry it took a while to merge!