add RSA PKCS1 signing (and structure for PSS + verification)
some style fixes
fix pep8
add basic multibackend so we can do signatures using default_backend
keyword args
more pep8
remove rsa_cdata_from_public_key (unused until verify PR)
incorporate review feedback. kwarg!
rename PKCS1->PKCS1v15 & UnsupportedAsymmetricPadding->UnsupportedPadding
change the rest of the UnsupportedAsymmetricPadding instances
update multibackend with new PKCS1v15 class name
some style fixes suggested by pep8-naming
Merge pull request #684 from reaperhulk/some-style-fixes

Some style fixes suggested by pep8-naming
Added TOTP implementation and tests.
Added documentation for TOTP.
Small fixes
Fixed documentation based on alexs' comments.
Updated secret key description
Added method definitions to TOTP documentation.
Updated HOTP and TOTP doctests