Feature: Allow Sprite to be a circle

[crhallberg]

Drawing and collision done.

Closes #317.

[crhallberg]

Awesome feedback all around. I figured there were going to be deeper parts of the system that needed to be touched, thank you for laying it all out so nicely!

[crhallberg]

Looking into these points, I wonder if it may be easier to use width and height throughout like the current objects and only check for radius in draw and collision and maybe keep it updated.

[straker]

Possibly as a first pass that might be OK. Without the GameObject handling the radius, any collision checks that involve scale would be off. But I can take care of that in another PR if you just want to add the initial work of letting a sprite have radius and drawing a circle instead of a square.

[straker]

@crhallberg Do you need any help with the pr?

[crhallberg]

I'm just busy at the moment. I'll take a look soon and let you know!

[straker]

Didn't hear back from you, so went ahead and did the work in a differnet pr.

Completed in https://github.com/straker/kontra/pull/404