Remove dependency on Flash

[zommerfelds]

I'm trying to use box2d in my Heaps.io project, compiled for HashLink. The compilation fails because of the usage of flash.display.Sprite in B2DebugDraw.

Since I probably don't need debug draw I was wondering if we can wrap this code around a compile flag (using #if swf or maybe a custom debug_draw flag).

I'm pretty new to Haxe, but since this seems like an easy PR I could look into it if you like the idea.

[zommerfelds]

Woops I just noticed that this might have been fixed already. However it is not included in the latest release.

Can we cut a new release? 1.2.3 seems very old.

[zommerfelds]

Still at 1.2.3 :(