Some small improvements to struct pointers
Implemented Sizeof instruction
Added a partially working performance test for Vector3 math
Generate Pointer.addElement instead of Pointer.add so that addition doesn't have to invoke GetNativeSizeOf
Fix CacheTypeExpressions accidentally mixing up type references
Prefetch the marshaller/unmarshaller when constructing a struct pointer so that it doesn't have to be fetched on every get/set
Generate more efficient closures for marshaller/unmarshaller functions