Add resize to bindings generated by register_vector.

register_vector currently generates push_back, size, get, and set. This is sufficient for growing vectors, but provides no way to delete elements and shrink vectors.  This change adds resize, which can be used to shrink vectors.

This is my first contribution, so I added myself to AUTHORS. I tried to follow the Contributing guide, and I welcome your feedback and help if I missed something.

Last, thank you very much for emscripten! This is really mindblowing!