interval/disjoin implementation

[joda]

Hi!

I see that disjoin is only partially implemented, but there's still code that looks interesting in the TODO comment. Is it a work in progress or is that something that you would like to see a PR for?

[joda]

Actually, we're no longer in need for disjoin. We found interval/difference, and that does what we need.

What is the intended difference between interval/disjoin and interval/difference though?