* Improve dev tools in the nix environment
Added postgrest-build, postgrest-run, postgrest-clean, postgrest-check
and postgrest-watch tools. Changed order of postgrest-test-spec-all to
run backwards from pg13 to pg9.5. Added shellcheck to lint shell scripts
in nix environment.
Co-authored-by: monacoremo <monacoremo>
Wolfgang Walther