optimize byte swap in base62 encoding (segmentio#50)

Co-authored-by: Tom Hacohen <[email protected]>

add go.mod

uint128 ops are much faster without loops. (segmentio#36)

Fix issue 25 (segmentio#26)

* fix panic on parsing invalid KSUID representations

* more tests

* cleanup

Fix issue 25 (segmentio#26)

* fix panic on parsing invalid KSUID representations

* more tests

* cleanup

Fix CompressedSetIter when set ends in a sequence (segmentio#24)

Fix CompressedSetIter when set ends in a sequence (segmentio#24)