Rebuild the nix flake; drop htoml dependency

[acowley]

Significantly simplified nix flake setup.

Replaced the htoml dependency in the spec test with tomland.

Fixes #172

[acowley]

Any thoughts on this @idontgetoutmuch? I took out a lot from the flake, perhaps too much, but I really wanted it to work with cached packages.

[idontgetoutmuch]

Any thoughts on this @idontgetoutmuch? I took out a lot from the flake, perhaps too much, but I really wanted it to work with cached packages.

Thanks very much for doing this :-)

I don't count myself as able to comment on nix. I don't use flakes (I know I ought to). I assume you were trying to test with previous version of ghc as well as the "current" one. I don't understand the user base of Frames well enough to know whether this is worth it.

[MMesch]

Hey, this is nice. Would be good to have frames available in upstream nixpkgs again.