Problem: lack details of _command method

Solution: generate a more accurate documentation header.
Merge pull request #184 from jemc/master

Problem: No way to insert arbitrary message tracing functions in server.
Problem: still refers to 'dictionary' in some places

Solution: use correct 'hash', especially in skeleton msg example.

Fixes #159.
Merge pull request #185 from hintjens/master

Minor fixes
Problem: loses messages on client destruction

This happens because we use two pipes. Solution: flush the msgpipe
before continuing with destruction. If client does a proper handshake
to sign off at server, this guarantees all messages are delivered to
server before destruction is finshed.
Problem: hangs on client shutdown

There are a few different cases; on interrupt, shutdown must not
do any handshaking, as ZeroMQ is terminated and messages won't be
delivered. On normal exit, shutdown must handshake, to not lose
any messages in flight.

Solution: handshake shutdown, unless interrupted, or actor is null,
indicating connection failed.
Merge pull request #186 from hintjens/master

Fixes to shutdown handshaking