Initial work on a prioritized multibackend for which implements CipherBackend
HashBackend is now supported by PrioritizedMultiBackend
Added support for HMAC backend
Added PBKDF2HMAC support
Replace re-running all tests with some unit tests
Direct tests for the cipher support
Direct tests for the hash support
Only make teh default once
Not true anymore
More direct tests
Fix
pep8 fixes
Refer to the `d` param of RSA as `private_exponent`.
Merge pull request #551 from public/pep8-link

Use python.org instead of peps.io
Merge branch 'master' into private-exponent
Merge pull request #550 from alex/private-exponent

Refer to the `d` param of RSA as `private_exponent`.
Use the builtin role to link to peps
hkdf
Refactor HKDF support and provide vectors for tests.
This got split into SHA1 and SHA256