Remove support for stack and make, align with current nixpkgs
A few noteworthy changes:
* Drop support for using stack or make. I never really needed these
and if you have a cabal file everything else should just work.
* Stop overriding base Haskell packages. This means that both
nix-build and nix-hs use the exact same dependencies. Once you
build them with either tool, the other doesn't have to do
* The default.nix file is now a proper package file. The previous
version which was an overlay is now in overlay.nix
* The -H option now *enables* haddocs and the new default is to
disable them. This makes nix-hs compatible with haskellPackages.
* If a project has a `nix/nixpkgs.nix' file, load it and use it
instead of doing an `import <nixpkgs>'
Actually enable profiling, new flag to disable Haddocks
* When building interactively, the `-p' command line option now
correctly enables profiling.
* New command line option `-H` to disable building Haddocks
globally. Helps when too many packages have missing/invalid
Haddocks and this breaks the build.