Enemy choosing

[xurxodiz]

There are several kind of enemies. They are all different.

For instance, turtles can kill other enemies, spikys can't be jumped upon, cannons are extremely hard.

Cannons are a good hint of being playing in higher levels of difficulty.

And turtles and goombas can be winged, being harder to face.

Should we implement the enemies as different states in the automaton (#16)? Or just one state, and in it pick by a different criteria, or randomly (bad idea) which enemy to place?

Reflect upon this and decide.

[xurxodiz]

Perhaps we can implement a common entry-state for enemies, from it transition with probabilities to either red turtle, green turtle, or goomba, and transition back to a common exit-state.

Cannons most probably need to be implemented as a separate element, as well as piranhas (from tubes, with certain probability).

[xurxodiz]

Cannons and piranhas are separate now, and the three other (red/green turtles and goombas) most probably will be in separate states depending on situation (turtles only make sense with other enemies, goombas can be alone).

[xurxodiz]

Merging it into #47.