Replace println() with println!() now that the former no longer exists
Convert the padding modes into a enum
Create ctr_enc() and ctr_dec() to create Encryptor and Decryptor trait objects
Commit 1
Commit 2
Commit 3
Commit 3 - mostly working.
Commit 4 - many fixups
Remove uncessary 'priv'
Minor example utility cleanups
Add in a (very slow) unit test