Version Update 1.53

- Significantly change the enemies' sniping shots.
- Small enemies will shoot correctly when stopping on the top of screen.
- Bullet speed difference in different difficulty is reduced, while the base bullet speed is increased.
- Ending bonus score will be affected by difficulty factor as well.
- Rank will not increase number of bullets any more.
- Rank now equals multiplier / 8.0 plus style rank.
- The period between each boss pattern has been increased.
- We haven't figure out how to change Boss Phase 2, for now we will nerf each pattern of Boss Phase 2 a little bit.
- UI changes, difficulty selection is more obvious.