Added context middleware support
Copyrights are changed
pep8 rule was fixed after previous commit
Updaing exceptions with OpenStack style

Reason:
 - Rewriting exceptions with OpenStack-exception-style.
Merge pull request #1 from crazymac/exceptions

Updaing exceptions with OpenStack style
Naming corrected
Merge pull request #2 from zaletniy/master

Naming corrected
Part of Storage Interface added
Naming corrected. flake8 check passes now
Added links to external resources
Merge pull request #3 from zaletniy/master

Naming corrected. flake8 check passes now
Storage interface implemented
Merge pull request #4 from Mirantis/storage-interface

Storage interface implemented
Cassandra python driver dependency added

And first steps of cassandra storage implementation were added
Merge pull request #5 from Mirantis/storage-interface

Cassandra python driver dependency added
Storage implementation skeleton fixed
Merge pull request #1 from Mirantis/storage-skeleton-fix

Storage implementation skeleton fixed
Merge pull request #7 from Mirantis/storage-skeleton-fix

Storage implementation skeleton fixed
Storage interface fixed

select_item, update_item methods were changed to meet DynamoDB
requirements
list_table api method fixed