Curved edges support

[RazinShaikh]

[jvdwetering]

So I know that @akissinger has an opinion on this, and I think I agree with him: if we go the interpolation route, it is much harder to exactly get the curve you want. Tikzit's bezier curves are much easier to get the curve you want. (although I think Aleks also disagrees with the need of this feature in ZXLive anyway)