Streamline development environment setup.

- Move test requirements into setup.py.
- Add shell.nix.

README.md

@@ -29,8 +29,6 @@ Running Tests
 -------------
 
 ```sh
-cd /path/to/mkcodes
 python setup.py develop
-pip install -r test-requirements.txt
 ./test
 ```

setup.py

@@ -3,6 +3,7 @@
 setuptools.setup(
     name='mkcodes',
     install_requires=['click'],
+    tests_require=['markdown'],
     extras_require={'markdown': ['markdown']},
     py_modules=['mkcodes'],
     entry_points={'console_scripts': ['mkcodes=mkcodes:main']}

shell.nix

@@ -0,0 +1,25 @@
+let
+  pkgs = import <nixpkgs> {};
+  testDependencies = [
+    pkgs.python3Packages.setuptools
+    pkgs.python3Packages.markdown
+  ];
+  mkcodes = pkgs.python3Packages.buildPythonPackage {
+    pname = "mkcodes";
+    version = "master";
+    src = ./.;
+
+    propagatedBuildInputs = [
+      pkgs.python3Packages.click
+    ];
+    checkInputs = testDependencies;
+
+    # FIXME
+    doCheck = false;
+  };
+in
+  pkgs.mkShell {
+    buildInputs = [
+      mkcodes
+    ] ++ testDependencies;
+  }