Motivation for this change

This adds makefile2graph, the ability to generate graphs from makefiles!

While doing this, I found the tests doesn't work properly because of a bunch of assumptions, so I didn't run them. It would require substitutions on the source first.

Furthermore I found that replace substitution make was conflicting on substitutions on make2graph. So I separated them into 1 substitution, and the other was a wrapProgram. Any advice on simplifying this?

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• [] Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.