Add `keep_last` to `consecutive_overlapping_subspans`?

[ericphanson]

Consider adding keep_last to consecutive_overlapping_subspans, or at least filing it as a feature request?

Originally posted by @hannahilea in #19 (review)

I think it is a bit hard to know exactly what those semantics should be when there's overlap. I guess something like: if there's 8 fold overlap, the last 7 will all be shorter than usual, and the last one will be 1 sample long. But it's a bit weird. I'd rather leave that until someone needs it.

@ericphanson in #19 (comment)

If you need this feature, here's a good place to say so!