1.9
   * Do not split MQTT packets over multiple calls to _client->write()
   * API change: All constructors now require an instance of Client
      to be passed in. 
   * Fixed example to match 1.8 api changes - dpslwk
   * Added username/password support - WilHall
   * Added publish_P - publishes messages from PROGMEM - jobytaffey

1.8
    * KeepAlive interval is configurable in PubSubClient.h
    * Maximum packet size is configurable in PubSubClient.h
    * API change: Return boolean rather than int from various functions
    * API change: Length parameter in message callback changed 
       from int to unsigned int
    * Various internal tidy-ups around types
1.7
    * Improved keepalive handling
    * Updated to the Arduino-1.0 API
1.6
    * Added the ability to publish a retained message

1.5
    * Added default constructor
    * Fixed compile error when used with arduino-0021 or later

1.4
    * Fixed connection lost handling

1.3
    * Fixed packet reading bug in PubSubClient.readPacket

1.2
    * Fixed compile error when used with arduino-0016 or later


1.1
    * Reduced size of library
    * Added support for Will messages
    * Clarified licensing - see LICENSE.txt


1.0
    * Only Quality of Service (QOS) 0 messaging is supported
    * The maximum message size, including header, is 128 bytes
    * The keepalive interval is set to 30 seconds
    * No support for Will messages