Begin work on implementing configuration interface

vcr/__init__.py

@@ -1,6 +1,7 @@
-# Import Cassette to make it available at the top level
-from .cassette import Cassette
+from config import VCR
+
+default_vcr = VCR()
 
 # Also, make a 'load' function available
 def use_cassette(path, **kwargs):
-    return Cassette.load(path, **kwargs)
+    return default_vcr.use_cassette(path, **kwargs)