release.nix: split out sources to reduce rebuilds

Having one source means that everything is rebuilt when e.g an
ihaskell-display package is modified. Splitting the sources out avoids
this by only rebuilding other packages that originate from the same
source.

release{,-8.2}.nix: run tests after build

Test with GHC 8.2

Now it tests with both GHC 8.0 and GHC 8.2

Work with GHC 8.2

Make silent and store_hitsory optional params

As per https://github.com/NixOS/nixpkgs/issues/29987

Nix improvements