Merge pull request #56 from agap/fix/crash-on-scan-restart

Fix a rare crash in BeaconScanner.

Merge pull request #53 from agap/fix/no-check-for-ble-adapter-on-stop

Change the BluetoothAdapter state check to be run only on Android 5.0.

Merge pull request #51 from agap/fix/clean-on-stop

Clean up the collection of nearby beacons when the Scanner's stop method is called.

Merge pull request #47 from agap/feature/beacon-update-events

Add beacon update callback.

Add sources.jar artifact to the release.