Add Adafruit_MQTT_Client class that implements MQTT code for generic Arduino client. Add ESP8266 example using new MQTT client class. Fix bugs with using library on ESP8266 (move CC3000 to header-only class).

Adafruit_MQTT_Client.h

@@ -0,0 +1,34 @@
+#ifndef _ADAFRUIT_MQTT_CLIENT_H_
+#define _ADAFRUIT_MQTT_CLIENT_H_
+
+#include "Client.h"
+#include "Adafruit_MQTT.h"
+
+// How long to delay waiting for new data to be available in readPacket.
+#define MQTT_CLIENT_READINTERVAL_MS 10  
+
+// MQTT client implementation for a generic Arduino Client interface.  Can work
+// with almost all Arduino network hardware like ethernet shield, wifi shield,
+// and even other platforms like ESP8266.
+
+class Adafruit_MQTT_Client : public Adafruit_MQTT {
+ public:
+  Adafruit_MQTT_Client(Client *client, const char *server, uint16_t port,
+                       const char *cid, const char *user,
+                       const char *pass):
+    Adafruit_MQTT(server, port, cid, user, pass),
+    client(client)
+  {}
+
+  bool connectServer();
+  bool disconnect();
+  uint16_t readPacket(uint8_t *buffer, uint8_t maxlen, int16_t timeout, 
+                      bool checkForValidPubPacket = false);
+  bool sendPacket(uint8_t *buffer, uint8_t len);
+ 
+ private:
+  Client* client;
+};
+
+
+#endif