vcr/unittest: Simplify file layout

.. and make "from vcr.unittest import VCRTestCase" work again.

vcr/unittest.py

@@ -0,0 +1,39 @@
+import inspect
+import os
+import unittest
+
+from .config import VCR
+
+
+class VCRMixin:
+    """A TestCase mixin that provides VCR integration."""
+
+    vcr_enabled = True
+
+    def setUp(self):
+        super().setUp()
+        if self.vcr_enabled:
+            kwargs = self._get_vcr_kwargs()
+            myvcr = self._get_vcr(**kwargs)
+            cm = myvcr.use_cassette(self._get_cassette_name())
+            self.cassette = cm.__enter__()
+            self.addCleanup(cm.__exit__, None, None, None)
+
+    def _get_vcr(self, **kwargs):
+        if "cassette_library_dir" not in kwargs:
+            kwargs["cassette_library_dir"] = self._get_cassette_library_dir()
+        return VCR(**kwargs)
+
+    def _get_vcr_kwargs(self, **kwargs):
+        return kwargs
+
+    def _get_cassette_library_dir(self):
+        testdir = os.path.dirname(inspect.getfile(self.__class__))
+        return os.path.join(testdir, "cassettes")
+
+    def _get_cassette_name(self):
+        return "{0}.{1}.yaml".format(self.__class__.__name__, self._testMethodName)
+
+
+class VCRTestCase(VCRMixin, unittest.TestCase):
+    pass