Boss attacks! They suck and will need to be rewritten, I just needed to get something out before I exploded.

entity.py: Introduce proper functionality in to the Boss entity: Can contain several BossAttacks, goes through each in turn as the timer runs out or their HP is depleted.
The system is flexible enough to allow for:
1) A single life bar, single attack
2) As many life bars as attacks
3) A single life bar with timed attacks (allowing the boss to timeout)
4) 2 and 3 combined
There's some nasty code to get it working, should (read: won't) revisit this.

handler.py:
BossScriptHp display for debugging purposes. Moved some code around to make sense

levels.py:
Boss attack test.

scripting.py:
Rewrote the 'createBoss' functionality to support the new multiple attacks, known as BossAttacks.
BossAttacks are formed of a script, a HP value and a timeout value. If provided, during a game:
1) Reducing an enemy attack to 0 HP moves on to the next script
2) Waiting for the timeout to expire will also move on to the next script

I kind of like the approach to scripts paired with HP and timeouts (which I've called an Attack), because we could feasibly apply it to enemies and players. We'll see what the future holds!

Next up I'll implement the idea of master/slave entities. That should help create some interesting scripts!
Note: It won't extend to multi-part entities quite yet, so bosses will still be just one entity rather than the
possibly multi-part monstrosities like in DoDonPachi.