Fix Enemy spawning

[Lol3rrr]

Problem

Sometimes while playing the game, it happens that the cactus and the bird, spawn so close to each other, that it's impossible to avoid both of them and there is no way around just loosing the game in that case.

Solution

The spawning algorithm should take the position of the other enemys into account and adjust the spawning accordingly, to allow the user to avoid them while not making everything too easy by simply spawning them too far apart.

[Lol3rrr]

This has been implemented in the latest commit to the Dev branch