Explicit backend
Add a default_backend and start updating docs.
Fix doctests.
Use backend as keyword argument everywhere.
Document all the parameters including cross references to specific providers where appropriate.
Test that openssl is the default backend.
Raise a correct error when content isn't padded correctly
Documentation!
One more documentation
Better, but still not covered
include the error message
Coverage
Change teh exception
Useful error message
Merge pull request #274 from alex/handle-bad-padding

Raise a correct error when content isn't padded correctly
Fixed branch coverage
Merge pull request #275 from alex/branch-coverage

Fixed branch coverage
Use keyword argument forms everywhere.
Put some docs for default_backend in a place.
Use backend as keyword even when copying hmacs.