Left handed perspective and lookAt functions

[amc522]

I split perspective, perspectiveFov, and lookAt into left handed and right handed functions. Each function is suffixed with LH and RH appropriately. The originally named functions default to calling the right handed function as to not change existing functionality. The default handedness of glm can be changed to left handed by defining GLM_LEFT_HAND.

[regnirpsj]

how about adding an enum or struct to express left-handedness or right-handed-ness (similar to std::nothrow_t and std::nothrow); this way overloading can be used to provide different versions.

[amc522]

Yeah, I could put in an overloaded function with an enum designating left or right handedness. As long as Christophe doesnt have anything against it.

[Groovounet]

The pull request looks great!
There isn't a precedent in GLM for overloading using an enum so I think this way is best.

Thanks for contributing!
Christophe