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
more kwargs
address review comments
reorganize docs slightly
some error msg improvements
Merge pull request #673 from reaperhulk/rsa-pkcs1-signature-only

Add RSA PKCS1 signing (and structure for PSS + verification)