Feat/2.1.0 release changelog documentation (#466)

* chore(changelog): add changelog for 2.1.0 release

* doc(rewind): add documentation a new feature `rewind` that can replay a cassette

* doc(exception): add documentation on the new behavior of the CannotOverwriteExistingCassetteException message

docs/debugging.rst

@@ -29,3 +29,29 @@ The second time, you will see::
 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.
+
+CannotOverwriteExistingCassetteException
+========================================
+
+When a request failed to be found in an existing cassette,
+VCR.py tries to get the request(s) that may be similar to the one being searched.
+The goal is to see which matcher(s) failed and understand what part of the failed request may have changed.
+It can return multiple similar requests with :
+
+- the matchers that have succeeded
+- the matchers that have failed
+- for each failed matchers, why it has failed with an assertion message
+
+CannotOverwriteExistingCassetteException message example :
+
+.. code:: python
+
+    CannotOverwriteExistingCassetteException: Can't overwrite existing cassette ('cassette.yaml') in your current record mode ('once').
+    No match for the request (<Request (GET) https://www.googleapis.com/?alt=json&maxResults=200>) was found.
+    Found 1 similar requests with 1 different matchers :
+
+    1 - (<Request (GET) https://www.googleapis.com/?alt=json&maxResults=500>).
+    Matchers succeeded : ['method', 'scheme', 'host', 'port', 'path']
+    Matchers failed :
+    query - assertion failure :
+    [('alt', 'json'), ('maxResults', '200')] != [('alt', 'json'), ('maxResults', '500')]