make README uptodate with the DHE-RSA support.
add simple method to get the certificate leaf.
default the version if not set which allow to report very early error (e.g. no cipher in common) properly
add a credentials module
add support for DSA signing and verification.
add support for DSS signature.
error in serverKeyXchg with RSA.
simplify the handshake key state.

we don't need to differentiate client/server, as a remote key will always be public and
the private key always local.
properly do DSS/RSA in DHE methods.
limit the X509 import list of what we need
use the new credentials system to be able to handle RSA and DSS certificate at the same time.
add a system to filter cipher that we can't use because we don't have the right credentials loaded.
add tests related to DHE DSS
limit to crypto-pubkey > 0.2.4
consistent style in record structure.
add new DHE-DSS ciphers
update utility with new ciphers and new credentials system.
generate DSA certificate and RSA certificate with proper extensions for tests
update TODO. DHE RSA+DSS is now supported.