Add Logging

This helps to figure out which matcher has decided your two cassettes
differ, and figure out when your cassettes have hit the network.

Closes #34

README.md

@@ -287,10 +287,44 @@ how to set this up.  I have marked the boto tests as optional in Travis so you
 don't have to worry about them failing if you submit a pull request.
 
 
+## Logging
+VCR.py has a few log messages you can turn on to help you figure out if HTTP
+requests are hitting a real server or not.  You can turn them on like this:
+
+```python
+import vcr
+import requests
+import logging
+
+logging.basicConfig() # you need to initialize logging, otherwise you will not see anything from vcrpy
+vcr_log = logging.getLogger("vcr")
+vcr_log.setLevel(logging.INFO)
+
+with vcr.use_cassette('headers.yml'):
+        requests.get('http://httpbin.org/headers')
+```
+
+The first time you run this, you will see:
+
+```
+INFO:vcr.stubs:<Request (GET) http://httpbin.org/headers> not in cassette, sending to real server
+```
+
+The second time, you will see:
+
+```
+INFO:vcr.stubs:Playing response for <Request (GET) http://httpbin.org/headers> from cassette
+```
+
+If you set the loglevel to DEBUG, you will also get information about which
+matchers didn't match. This can help you with debugging custom matchers.
+
+
 ## Changelog
   * 1.0.0 (in development) - Bump supported Python3 version to 3.4, fix some
     bugs with Boto support (thanks @marusich), fix error with URL field
-    capitalization in README (thanks @simon-weber)
+    capitalization in README (thanks @simon-weber), added some log messages
+    to help with debugging.
   * 0.7.0: VCR.py now supports Python 3! (thanks @asundg)  Also I refactored
     the stub connections quite a bit to add support for the putrequest and
     putheader calls.  This version also adds support for httplib2 (thanks