Nix-rebar3: Build Erlang/rebar3 projects by parsing lock files in pure Nix

Hi everyone!

nix-rebar is a Nix library for building rebar3 projects I have been working on recently. There already exist pretty good Nix options for Erlang, but as someone who prefers Nix builders such as naersk, napalm or mix-to-nix, I did not find anything like that for rebar3, and so this is that project. That is to say, instead of FODs or the approach taken in e.g. rebar3_nix where the tool generates a deps.nix file you check in to version control, nix-rebar will parse the rebar3 lock file directly using a parser for a subset of Erlang written in Nix.

The README also contains a short summary of the state of Erlang packaging in Nixpkgs, where I tried to sum up the up-to-date info from threads such as State of the BEAM Ecosystem in Nix. I would appreciate if anyone actually involved in that effort could look it through for any errors!