Add LenSqr functions

[Zyl9393]

Added SqrLen() functions which return squared vector length. This can make some lines shorter when variable names are long, e.g.:
worldSpaceFragmentCenter.Dot(worldSpaceFragmentCenter)
vs.
worldSpaceFragmentCenter.SqrLen()
Understandable if not wanted, though. Mostly learning how 2 github over here. Have a nice day.

[pwaller]

Sorry it has taken a while for someone to get back to you on this. I can't see anything wrong with this other than a minor bug in the automatically generated files. Can you rectify and I'll merge assuming there aren't any objections.

[pwaller]

Thanks for fixing the issues I raised!

One thing that occured to me as I go to merge it:

How about LenSquared as the name of the function? Then if you're using an editor with autocomplete, it will show up as you're looking for Len - improving the discoverability. Also it would appear next to Len in the documentation: https://godoc.org/github.com/go-gl/mathgl/mgl32

Let me know what you think. Happy to accept it as is otherwise - though I will squash the history down to just "Add ... functions", to avoid the merge commit going from master into the development branch.

[MMulthaupt]

I would expect autocomplete to list the function regardless of where in the name the substring is found, but regarding the documentation, you raise a good point. Maybe call it LenSqr then, or LenSq even? Having it short was one of main reasons for making this, and Sq is a well understood shortcut in anything math-related; even Java refrains from its usual verbosity, calling the square root function in its Math package sqrt.

[pwaller]

OK, then 👍 to LenSqr from me.

[Zyl9393]

Should be good now.