Update code to work with Requests 1.0.4

Requests codebase has been refactored significantly.
Updated code to work with the latest version of Requests.
Merge branch 'master' of https://github.com/meowcoder/requests-cache into v1.0.0
CachedSession without monkey patching. Backward incompatible
expire_after is seconds
fix some tests
hash instead url+data, begin fixing redirects
move key creation to cache, add attributes to stored response
fix delete(key)
make more tests compatible
url -> key
possibility to pass cache backend instance instead name
cleanups
clarify usage of key_mapping
response.history is tuple in Requests 1.x.x
fix instance check in CachedSession (str -> basestring)
move storage implementations to package
has_url() and delete_url() methods
fix thread_safety test
update Requests's required version
missed package in setup.py, bump version