working on version history
pass keys as interface{} rather than []byte

This will allow clients to pass, for example, their own instances of
rsa.PublicKey if the key is not specified as some flavour of X509
cert. For example, Salesforce just specify the modulus and
exponent (https://login.salesforce.com/id/keys)
cleanup and documentation updates
can now pass a PrivateKey to SigningMethodRSA.Sign

Conflicts:
	rsa.go
can now pass a PublicKey to SigningMethodRSA.Verify
expose RSA key PEM parsing funcs
make helper methods more specific
documentation fix
documentation