change serializer API so it doesn't have to do file stuff

vcr/serializers/jsonserializer.py

@@ -13,16 +13,15 @@ def _fix_response_unicode(d):
 		d['body']['string'] = d['body']['string'].encode('utf-8')
 		return d
 
-def load(cassette_path):
-    with open(cassette_path) as fh:
-        data = json.load(fh)
+def deserialize(cassette_string):
+    data = json.loads(cassette_string)
     requests = [Request._from_dict(r['request']) for r in data]
     responses = [_fix_response_unicode(r['response']) for r in data]
     return requests, responses
 
-def dumps(requests, responses):
+def serialize(cassette_dict):
     data = ([{
         'request': request._to_dict(),
         'response': response,
-    } for request, response in zip(requests, responses)])
+    } for request, response in zip(cassette_dict['requests'], cassette_dict['responses'])])
     return json.dumps(data, indent=4, default=_json_default)