Begin work on implementing configuration interface

vcr/config.py

@@ -0,0 +1,9 @@
+from .cassette import Cassette
+
+class VCR(object):
+    def __init__(self, serializer='yaml', cassette_library_dir=None):
+        self.serializer = serializer
+        self.cassette_library_dir = cassette_library_dir
+
+    def use_cassette(self, path, **kwargs):
+        return Cassette.load(path, **kwargs)