Update AUTHORS

Clarify current and previous maintainers, re-order with current maintainer on top
Merge pull request #22 from djmitche/patch-1

Update AUTHORS

Clarify current and previous maintainers, re-order with current maintainer on top
add isdisjoint
add IPSet.isdisjoint to README
Merge pull request #21 from djmitche/isdisjoint

Fix isdisjoint behavior