Add option to draw newer bullets underneath older ones

[ShadowCommander]

Fixes #233

Adds an option to projectile template for reversing the z index drawing order so that newer bullets are drawn beneath older bullets.

Ran a test with pool size 10,000. Lifetime 6s.

Average time in seconds of 1000+ samples.

	Reverse	Forward	Reverse no index var
Average	0.002010674033	0.001833547882	0.001846225853
Median	0.002	0.001808	0.001832

Original Reverse

var index = projectile_active_index[i]
draw_set_transform_matrix(projectile_instance_array[index].transform)

Old:

New with reverse_z_index enabled:

[ShadowCommander]

Signed the commits

[superhighlevel]

Thanks
The variable comment can be a bit clearer
Something like: Invert the rendering order of the projectile; the newer bullet will render behind the old one.