drop capslock, use {ChangeLog, ReadMe, License}.md (#831)

I know a couple of good people annoyed by capslocking.
And moreover, studies show it is harder to grasp the capslocked text.
Capslocking does not work anyway and not worth it, somewhere since we got Web & URLs.

hnix.cabal

@@ -8,7 +8,7 @@ bug-reports:    https://github.com/haskell-nix/hnix/issues
 author:         John Wiegley
 maintainer:     johnw@newartisans.com
 license:        BSD3
-license-file:   LICENSE
+license-file:   License
 build-type:     Simple
 cabal-version:  >= 1.10
 data-dir:       data/
@@ -19,6 +19,9 @@ data-files:
     nix/corepkgs/fetchurl.nix
     nix/corepkgs/imported-drv-to-derivation.nix
 extra-source-files:
+    ChangeLog.md
+    ReadMe.md
+    License
     data/nix/corepkgs/buildenv.nix
     data/nix/corepkgs/unpack-channel.nix
     data/nix/corepkgs/derivation.nix
@@ -270,9 +273,6 @@ extra-source-files:
     data/simple.nix
     data/nixpkgs-all-packages-pretty.nix
     data/let.nix
-    LICENSE
-    README.md
-    CHANGELOG.md
     tests/eval-compare/builtins.appendContext.nix
     tests/eval-compare/builtins.eq-bottom-00.nix
     tests/eval-compare/builtins.fetchurl-01.nix