more new test material
loading pubkeys and pubsubkeys works again
 - Reimplemented String2Key
 - Sped up String2Key.derive_key significantly by doing math instead of a dumb loop
 - Implemented {Pub,Priv}{,Sub}KeyV4
 - Moved implementation of key decryption to Priv{RSA,DSA,ElG}
 - Added series of unit tests to test parsing many types of String-To-Key data
 - Added new unit test to test decrypting encrypted key material
 - Copied some encrypted private keys from the old test material into the new test material set for testing the decryption of encrypted secret key material
 - Minor code organization changes to prevent stupid circular import problems