Fix typo related to intersections at endpoints

[bluenote10]

This PR mainly fixes a small typo in the translation of the JS algorithm to Rust. I already noticed that the Rust algorithm had a small difference compared to the JS on test case issue103. Basically it produced a spurious vertex next to another vertex. Not fully wrong, because it still followed the same shape, but not needed for the result:

Tracking down the issue turned out that it is simply a && that should have been || (see JS side here). I have also added a new test case:

Comparing the before and after coordinates at this case case, we can see that the spurious vertices around the correct vertices disappear:

I've also updated the readme a little bit.

[bluenote10]

@untoldwind Can we merge this as well? If you want me to more actively help you with maintaining this library you may give me some slightly extended rights so that I could merge minor changes like this without bothering you, and also to clean up the open issues a little bit, e.g. closing a few solved ones. I don't need/want direct push rights, because I prefer going through PR in general, and I would mainly ping you for more general changes especially if they touch Rust design questions if that's okay for you.