Modularized output, refactoring

Making it ready for output formatting plugin API.

tests/test_windows.py

@@ -2,8 +2,9 @@ import os
 import tempfile
 
 import pytest
+from httpie.context import Environment
 
-from tests import TestEnvironment, http, httpbin, Environment
+from tests import TestEnvironment, http, httpbin
 from httpie.compat import is_windows