Release 0.4.1

Release 0.4.1

This is a minor release.

Enhancements

* Introduce API GattServer::areUpdatesEnabled() to determine notification
  status for a characteristic.
  This is a follow up from https://github.com/mbedmicro/BLE_API/pull/41.
  @jeremybrodt did a lovely job submitting that pull request, but there had
  been too many changes in the neighbouring code recently to merge his
  work directly. I didn't take the trouble of preserving his submission
  in the history; my apologies--credit for this API goes entirely to him.

* Replace DiscoveredCharacteristic::setupOnDataRead() with GattClient::onDataRead().

* Move GATT_MTU_SIZE_DEFAULT into blecommon.h as BLE_GATT_MTU_SIZE_DEFAULT.

* Replace uses of the deprecated updateCharacteristicValue() with ble.gattServer().write().

* Change access levels to protected for various members of the standard services.

* Update LinkLossService with a recent change to the definition of
  GattWriteCallbackParams. Involved renaming member charHandle to handle.

Bugfixes

• None.