Added README for new 'all_played' property of Cassette
Added tests for Cassette#all_played
pep8
Added implementation for Cassette#all_payed
Update README.md
Update copyright date
lets try response headers as dicts
change response format
update migration fixtures
fix python3 compat
update wild cassette to match new format
remove some unused serialization code
fix migration script
fix python3 compat
Make Serializers Dumber

Let's have the serializer just worry about serializing the dict
that we hand it, and move the unicode stuff up to a serialize module.

This should hopefully let us move toward using a version string in
cassettes.
fix a couple imports for py3
update serializers
update old cassette detection
flickr test was actually using yaml cassettes
not really very happy about this