Support for multiple ellipses, as per PS #506

[david-pfx]

Take a look at PS increpare#506 and the corresponding commit.

1. The code changes are major.
2. Due to refactoring it ain't gonna merge, or at least not without much pain.
3. The benefit is small -- who uses it and what's it for anyway?

Thoughts?

[ClementSparrow]

It does not seems like a huge commit to me. But it seems to be a lot of ad hoc code just to deal with the 2-ellipsis case, and I think it would actually be simpler and more clean to deal directly with the general case. Also, I would change the data structure of rules to represent a square bracket pattern as a list of ellipses-separated patterns instead of having ellipses represented as special cells in a pattern. This would also make the code much cleaner and easier to maintain. So, this is one of these features that I'd like to re-implement the P:S way rather than just merging the commits from vanilla PS.

[david-pfx]

Not huge, but big enough to be sure there will be bugs. I was expecting ~10LOC, not 100+. It just isn't worth that amount of effort.

And yes, if it's worth doing it's worth doing with generality.

But I think you just assigned it to yourself, so I move on.