v1.0.0 release!

A small change from v0.9.17 is the addition of another
"shellcheck disable=". Otherwise it is identical.
v0.9.17 has been stable and no bugs have been found over
prolonged use, so that's as good a reason as any to
declare the API stable and signal a proper release

Add conditional disable=SC2154, fixed #16

* Try both shasum and sha256sum when generating doc checksum

* Do not fail when unable to compute shasum of DOC
* Fix quoting of escaped variables in DOC
* Reduce parser by 1 line
* Show STDIN as source on errors when not using script path argument
* Support bash 5
* Fix bug when running on script without DOC=