added

flake.nix added to repository, allows directly running nix-index from
git (#162), thanks @matthewbauer
support for proxies (#132), thanks @whizsid
command-not-found.sh suggests new nix profile command if
manifest.json exists (#135), thanks @matthewbauer
support building project via Nix on Darwin (#175), thanks @BrianHicks
indexer supports prefix filtering (#177), rhanks @virchau13
command-line option to specify system for which to build the index
(#183), thanks @usertam
nix-channel-index: new command to build a programs.sqlite as currently
distributed with nix channels (#192), thanks @K900

fixed

command-not-found.sh never accesses undefined variables anymore
(allows set -u) (#123), thanks @matthewbauer
support xlibs renamed to xorg in recent nixpkgs (#179), thanks @cole-h
rust dependencies updated to latest versions, fixes security warnings, thanks @edude03,
@berbiche, @Sciecentistguy, @Mic92

nix-env is now invoked in parallel to query paths (improves
performance)
performance improvement: multithread compression (#152), thanks
@enolan
performance improvement: reduce compression level from 22 to 19
(#152), thanks @enolan
performance improvement: get store paths from nix-env in parallel
(#152), thanks @enolan