add mat2d
fix mat2d operations, update tests
add a benchmark for mat2d
fix some 2d operations
Merge branch 'master' of https://github.com/toji/gl-matrix

Conflicts:
	gl-matrix.js
Add mat2d spec and some missing functions

Added specfile for mat2d
Add vec2.transformMat2d
Add mat2d.translate
Merge pull request #60 from rbeitra/master

2x3 Matrices for affine 2d transforms