feat(quat): optimize quat_mul for SSE2 by using XOR to flip the sign bit
feat(quat): optimize quat_mul for SSE2 by using XOR to flip the sign bit

See https://github.com/nfrechette/rtm/issues/29

nfrechette/acl,nfrechette/acl,nfrechette/acl,nfrechette/acl,nfrechette/acl