Added set functions for matrices

Various mat*.set* for translations, rotations, and scaling. The 'a'
argument has been removed and instead they operate on an implicit
identity matrix, drastically reducing the number of mat*.identity calls
required in some scenarios.
Add from functions for matrices

Replaced the previous commit since it was poorly done and didn't follow
established convention. Also added comments.

Various *mat.from* for translations, rotations, and scaling. The *a*
argument has been removed and instead they operate on an implicit
identity matrix, drastically reducing the number of *mat.identity* calls
and trivial 1 and 0 multiplications required in some scenarios.
corrected typo: setScale is now setScaling in mat2
corrected typo: setScale is now fromScaling in mat2
Merge branch 'master' of https://github.com/drdeath863/gl-matrix
Merge pull request #145 from drdeath863/master

Added fromRotation/Scaling/Translation functions for matrices