Neon support, perf improvements and fixes for warnings

Hi, a couple of us in Google have made a few modifications to vectorial.  We hope you're able to merge the following patch series:
* Support for SSE1/2
* Fix for gcc narrowing conversion warnings
* Return of determinant from simx4x4_inverse to detect matrices that can't be inverted
* Perf improvement for dot product, cross product and vec3 store
* 2f NEON implementation

Cheers,
Stewart