Interceptor Demo update 2021-09-30

Update 2021-09-30:

• Added delayed spawn to enemies and modified a few spawns to show this earlier in the game.
• Added basic score keeping that total number of ships killed at the end of a level.
  • Game does track kills by ship type in background, but a way to show or value these kills is still being worked out.
• Moved Earth fleet splash art to level 3 and added text that reads “press start” to that screen.
  • Eventually art will be assembled for the first two demo levels and eventually all levels.