Previously the code would send pings only when SocketSelect() would
timeout. This was not working when a client was subscribed to a topic
and would receive periodic messages but wouldn't itself send anything.
This meant that SocketSelect() wouldn't timeout at any point and we
wouldn't execute the check for sending a PINGREQ.

The fix is to do the check for last sent packet before calling
SocketSelect() so that if we haven't been sending anything for a while,
we really send the PINGREQ.

Fixes #10

* the-great-refactor:
  Add big_message_test
  Fix publish message serialization
  Modify the code to use nonblocking sockets
  Fix indentation
  Free userName and password in MqttClientFree()
  Add forgotten files
  Massive refactoring of the internals

The test tries to publish and receive 3.5 megabyte message.

All of the publish messages regardless of qos contained the message id.