[Breaking] Add disconnect reason to client callback. (#398) (#81)

Adds the reason code as a parameter to the client onDisconnect callback.

* Update examples/docs.

examples/basic/BLE_client/main/main.cpp

@@ -43,7 +43,9 @@ class MyClientCallback : public BLEClientCallbacks {
   void onConnect(BLEClient* pclient) {
   }
 
-  void onDisconnect(BLEClient* pclient) {
+  /** onDisconnect now takes a reason parameter to indicate the reason for disconnection
+  void onDisconnect(BLEClient* pclient) { */
+  void onDisconnect(BLEClient* pclient, int reason) {
     connected = false;
     printf("onDisconnect");
   }