remove unnecessary call to Normalize().

honor closest distance in quaternion slerp

Fix the quaternion spherical linear interpolation
to make it choose the shortest linear path, which
is the intended behavior in graphical animations.

GitHub-Pull-Request: #90

Merge pull request #82 from aykevl/vec4-quat

Add Vec4.Quat() method to reinterpret a vec4 as a quaternion

Added autogeneration disclaimer headers to matrix and vector files.