Nix files.

These new Nix files can be used as an alternative to the Stack-based
build.

Change-Id: I56ae4e27fa26541cd88583a7806f2834cb6a1735
diff --git a/.gitignore b/.gitignore
index 4353b27..184e972 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 *.iml
 
 /config.dhall
+/result
 
 /.idea
 /.stack-work