New Update: Shoving, mouse controls and various tweaks

I just uploaded a new update:

- You can now shove your opponent away by double tapping forward while holding the attack button.

- Holding your attack lets you charge up your movement speed when you release it. This will replace the dash for now.

- The game can now be played using a keyboard and mouse. Move the mouse up and down to aim your sword.

- Sprite tweaks: Slightly improved the character's posture and added some new sprites for when your attack has been blocked.

- Rebuilt the menu from scratch. It's still visually very basic but it should be easier to navigate.

- A new stage plus some variations on the Temple stage.

- Added some ambient music to the combat.

- Your sword is now stained red after getting a kill.

Let me know if I broke something.