0.9.2 release add connected function

Add connected() function to MQTT class to provide a way for clients to check if they are connected to the MQTT server or not. This is useful for reconnecting when on an unreliable network. CC3k and ESP8266 examples are updated to show using the connected function to reconnect automatically in their main loop.

Also updated examples to set the MQTT client ID using the date and time the sketch was compiled (in addition to the AIO key). This is useful to prevent issues with multiple clients from the same user running at the same time (if they had the same client ID they would have contention over receiving MQTT messages).

Bug fix for snprintf on non-Arduino platforms

Small release to fix bug with using snprintf on non-Arduino platforms like the ESP8266.

Initial release.

Initial release with support for CC3k, ESP8266/generic Client interface, and FONA.