add API BLEDevice::shutdown() to purge the BLE stack of GATT and GAP state.

init() should be called before restoring state.

fixes #15.

common/BLEDeviceInstanceBase.h

@@ -28,6 +28,7 @@ public:
     virtual Gap&        getGap()                   = 0;
     virtual GattServer& getGattServer()            = 0;
     virtual ble_error_t init(void)                 = 0;
+    virtual ble_error_t shutdown(void)             = 0;
     virtual ble_error_t reset(void)                = 0;
     virtual ble_error_t setTxPower(int8_t txPower) = 0;
     virtual void        waitForEvent(void)         = 0;

public/BLEDevice.h

@@ -36,6 +36,11 @@ public:
     ble_error_t init();
     ble_error_t reset(void);
 
+    /**
+     * Purge the BLE stack of GATT and GAP state. init() must be called afterwards to re-instate services and GAP state.
+     */
+    ble_error_t shutdown(void);
+
     /* GAP specific APIs */
 public:
     /**
@@ -364,6 +369,13 @@ BLEDevice::reset(void)
     return transport->reset();
 }
 
+inline ble_error_t
+BLEDevice::shutdown(void)
+{
+    clearAdvertisingPayload();
+    return transport->shutdown();
+}
+
 inline ble_error_t
 BLEDevice::setAddress(Gap::addr_type_t type, const Gap::address_t address)
 {