Revert "Add combinators"

This reverts commit 9abae5e6bc3b0f71f2bef38043796333559eaf00.
Fix E23 bug and re-enable E23 CI
Add dash-functional back, now dependent on dash.el

- instead of the other way around
Add docs about require for dash-functional
Update -max-by & friends
Add anaphoric example to --max-by and --min-by
Release 2.0.0
Update docs too