Cleanup and improvement for fromVectors()

[infusion]

Hi Stefan,

thanks for Cannon.js! As I am the author of Quaternion.js ( https://github.com/infusion/Quaternion.js ), I was interested in your implementation and figured, your fromVectors() method could be improved quite a bit. Besides this I added a note where the calculation for normalizeFast() comes from and removed the unused vectors used before for multiplication.

Hope this is helpful. Robert

[infusion]

Is the project still alive?

[kungfooman]

Is the project still alive?

Not exactly this repo, but I'm still using and updating the code for myself. I was actually wondering just some days ago how Quat#normalizeFast works and now this appeared in my issue list again because of your question :see_no_evil: Thank you!

[infusion]

It should maybe not be called normalizeFast, but more like refineNormalization or something, since this also reflects the use case of having a normalized quat already that may need some adjustment