Alpha update

I wanted to try out something again in Pico-8, and went out adding a new ship/character to choose from.

Currently you can now play as a low-poly android called Alpha:


Alpha uses two sentinel guns that shoots right next to her, her shooting speed is the same as the lasership, but it's more spaced out.
However, if you're moving forward, then the sentinels gets a focussed fire, and then shoot as fast as in hypermode, she can also use it when moving backwards to stay in place, but she cannot move left or right with it. This allows her some utility to fight enemies on multiple ways.

Some other changes include:
- Visible names on the ship selection screen, based on their XNA ship names.
- A sound effect when scrolling through the menu
- Buffs to the purple Catapult ship, so a single shot can take down a green alien, as well as a new unique hypermode.

Update v0.3.1
- Changed the Catapult's hypermode to make it more laser-like, it now also has progressive upgrades depending on the ship's level.

And that's all from now, hope you'll enjoy this small update