Add support for self-intersecting rings that touch themselves, but don't cross

[mfogel]

Add support for self-intersecting rings that touch each themselves, but don't cross.

Rings of this form are guaranteed not to be ambiguous with respect to the even-odd rule and the non-zero rule.

Examples of rings that just touch each other, but don't cross:

• Bow tie that intersects itself but doesn't cross
• ring-within-ring that intersects itself but doesn't cross

Examples of self-intersecting rings that cross themselves:

• Bow tie that crosses itself
• ring-within-ring that crosses itself
• ring-within-ring that loops twice