Check out if we could use a GHC source plugin

[picnoir]

Instead of using the current build process, ie.

1. Build the package using stack.
2. Retrieve the dynamic flags using cabal-helper.
3. Load the modules in GHC API using these flags

Investigate GHC source plugins to see if we could use them to ditch step 2. This would reduce the number of moving parts.

Potential side effect: this would also fix #8 and allow us to run the tests directly from nix-build.