Update docs and comments

Author: balsoft

changelog.md

@@ -1,6 +1,9 @@
 This file contains a summary of changes to Haskell.nix and `nix-tools`
 that will impact users.
 
+## December 10, 2019
+  * Now the `cache` attribute of `stackProject` is not required and is going to be deprecated.
+
 ## November 18, 2019
   * Changed the `cleanSourceHaskell` to accept an attrset of `src` and
     (optional) `name` parameters. This allows you to keep the source

overlays/haskell.nix

@@ -259,8 +259,6 @@ self: super: {
             # src value.
             #
             # TODO: this should be moved into `call-stack-to-nix`
-            #       it should be automatic and not the burden of
-            #       the end user to work around nix peculiarities.
             { packages = builtins.foldl' (x: y: x // y) {}
                 (builtins.map ({ name, url, rev, sha256, subdir ? null, ... }:
                     { ${name} = { src = self.buildPackages.pkgs.fetchgit { inherit url rev sha256; }; }