Make interval equality operator compare start and end of intervals

[jakemanger]

An approach to Fix #1135
This changes the default behaviour from comparing the interval duration to comparing the start and end of the interval, which I believe is more intuitive (it has slipped me up before). However, would this require a warning to notify users that the default behaviour has changed?

[vspinu]

Hi @jakemanger, there is a failure in pkgdown. I think you need to declare it in the index.

More importantly, Should we add inequalities as well, for full partial order implementation?

Also could you please test for vectorized operations, not just single-tons, and add a new-features news entry?

Thanks!!!

[jakemanger]

Hi @vspinu I've declared == and != in the index and have added inequalities and vector support. That vectors test was important, as I had used && previously where & is needed for vectors. I am running into an unusual issue with the tests of vctrs now. I haven't edited any part of that in the project. Do you know why this could be happening?