Parse and serialize rules.json

TL;DR:
- Write FromJSON instances to decode rules.json file
- Prefer Text to String and use the OverloadedStrings language extension
- Read /etc/hosts and append the serialized rules.json to the end

Notes:
- I can remove some of the FromJSON instances and use GHC Generics to define
  them for me.

TODO:
- Define the systemd timer unit for this to run
- Ensure script can run with root privileges

tools/website-blocker/shell.nix

@@ -2,7 +2,11 @@ let
   pkgs = import <unstable> {};
 in pkgs.mkShell {
   buildInputs = with pkgs; [
-    ghc
-    haskellPackages.time
+    (haskellPackages.ghcWithPackages (hpkgs: with hpkgs; [
+      time
+      aeson
+      either
+      hspec
+    ]))
   ];
 }