Changed all inner types to a more peformant (static) structure by default.
This changes the way casts work in that other types can no longer be
auto-casted without copying. To use the old behavior specify -D
HXMATH_USE_DYNAMIC_STRUCTURES. This addresses issue #16 and brings the
ratio between abstracts vs. hardcoded inline functionality down to
2x~0.75x (nearly comparative performance).