add Plane.intersectLine with unit tests.
expand Matrix3 with set, identity, copy, multiplyScalar, deteminant, clone;  Matrix3/4.getInverse will now optionally throw an exception; start Matrix3/4 unit tests
remove debugging log message from Matrix3.getInverse
optimize determinant calculation in Matrix4.getInverse()
add credits.
fix Raycaster instance references to use Raycaster.ray
expand tests of Matrix3 and Matrix4 inverse functions.
Simpler CONTRIBUTING suggested by @WestLangley. Fixes #2847.
Docs: Updated structure.
Merge remote-tracking branch 'maxogden/pointerlock-bugfix' into dev
reorder Matrix4.determinant to match order used by Matrix4.getInverse
pull out common factors of Matrix4.determinant.
add another determinant unit tests which utilizes every value of the matrix.
reorder based on @WestLangley suggestion.
remove unused variables from Raycaster.
add Plane.flip() plus unit test.
add Frustum.containsPoint, containsSphere + first Frustum unit tests.
polishing frustum to a first class member of math.
more Frustum unit tests + minor optimization to Plane.
always use local var planes = this.planes in Frustum. fix common include to require Sphere before Frustum.