Nameplates are never released #65

Although #21 hints at this ("release is not exported"), one underlying protocol issue is that we never release the nameplates.

This, for example, can cause spurious "crowded" error or cause the Python client to "never exit" on text-message sending.

It would be ideal if the library called "release" at the right moment, but that may be beyond my Haskell skills at the moment.

That "right moment" is immediately after we have the PAKE message.