Added projectiles

They are shitty 1) because of quick implementation, for example I need
to fix the fact that they are using grid positions to calculate things
and firing from the top left of each object, 2) because (per your
earlier suggestion) we should figure inheritance from a superclass that
has location properties and rendering at least and an actual destructor.
Its gettin hairy without it.
For now it looks a bit like a nice AOE tower (think Spike thrower/ Ring
of Fire)
Merge branch 'master' of https://github.com/futesobriquet/Tower_D_beta