Triggers and level ending

[Eero Tamminen]

Hi,

I've added an initial trigger object implementation and a few trigger types
to Airstrike SVN.

Levels 0 & 1 contain now demonstrations of how level-done and level-fail
targets are triggered, and more information you can get by going to the
Airstrike shell and typing "trigger".


There are still a couple of problems:
- How I call (message) an object to which I have only an ID (or tag)?
  Ulf?
- I would like to schedule trigger object events, but currently only sprites
  have a convenience function for this.  Would it be possible to move
  schedule to core, and have a convenience function for message sending
  scheduling?  Ulf?
- I haven't tested all the trigger types I coded yet,
  I will do that next week

TODOs:
- Proximity trigger is still missing and will/would be very nice.  I'll
  look into this once the other stuff is tested/ready
- Game should show in the window whether level ended succesfully.
  I guess level should restart if it failed... :-)
- Rest of the levels should have level-done/fail triggers too
- I was also thinking that plane should suicide if user tries to bomb, but
  there's neither more bombs nor fuel, would that be acceptable?
  I though to add level-fail condition to planes dying too many times to
  each level.  Other alternative would be to just have a "Restart level"
  key.  Opinions?


	- Eero