simplify enc/dec in the OpenSSL backend by using the EVP_Cipher* methods
Merge pull request #175 from reaperhulk/evp-cipher-methods

[WIP] Simplify Cipher Encryption/Decryption Interfaces in OpenSSL
Give  API collections direct references to the backend.
Merge pull request #177 from dreid/privatize-cyclical-backend

Give API collections direct references to the backend.
Initial refactoring of backend specific contexts.
Don't forget to provide an interface.
AES GCM vectors from NIST

* http://csrc.nist.gov/groups/STM/cavp/documents/mac/gcmtestvectors.zip
Rename _OneTimeCipherContext
Merge pull request #178 from dreid/composable-contexts

[WIP] Reduce the backend's API surface by making it a vendor of implementation specific CipherContext providers.
Merge pull request #179 from reaperhulk/gcm-vectors

AES GCM vectors from NIST
Also linkcheck the docs
Update the requirements file for our direct invocations of coverage
Merge pull request #185 from alex/linkcheck

Also linkcheck the docs
Merge pull request #186 from alex/reqs

Update the requirements file for our direct invocations of coverage