Add the option to provide a secret expiration date when creating orders

Make aes the default algorithm option
Merge branch 'master' of https://github.com/cloudkeep/python-barbicanclient

* 'master' of https://github.com/cloudkeep/python-barbicanclient:
Update keep to comply with the MIME type revamp

Also bump the version
Modify client library to comply with MIME revamp
Make payload_content_type in keep default to
'text/plain' for secrets and 'application/octet-stream'
for orders, and stop constraining the content options.

Stop displaying payload_content_type when displaying secrets.
Modifications to reflect payload_content_encoding being required
for order creation

Update tests to comply with MIME type revamp
Modify default behaviors and the create_order signature
Remove payload_content_encoding from orders
Change the lookup method for Secret dict fields
PEP 8/Pyflakes fixes
Merge pull request #15 from Aghoreyshi/master

Update the client library and keep to comply with the MIME type revamp (merged on behalf of Doug!)