Add .default.nix and .envrc

.default.nix

@@ -0,0 +1,19 @@
+with import <nixpkgs> {}; {
+  autocmakeEnv = stdenv.mkDerivation {
+    name = "Autocmake";
+    buildInputs = [
+      atlas
+      ccache
+      clang
+      cmake
+      doxygen
+      gfortran
+      liblapack
+      openmpi
+      python35Packages.pep8
+      python35Packages.pytest
+      python35Packages.pyyaml
+      zlib
+    ];
+  };
+}

.envrc

@@ -0,0 +1,7 @@
+use nix .default.nix
+export SOURCE_DATE_EPOCH=$(date +%s)
+dir_hash=autocmake-$(echo -n autocmake | shasum | cut -d ' ' -f 1)
+direnv_layout_dir=$XDG_CACHE_HOME/direnv/layouts/$dir_hash
+layout python `type -P python` --system-site-packages
+pip install -r requirements.txt
+export NINJA_STATUS="[Built edge %f of %t in %e sec]"