[Reference]
  1. how to open bluetooth settings in android?: http://stackoverflow.com/questions/13911468/how-to-open-bluetooth-settings-in-android
    Intent intentOpenBluetoothSettings = new Intent();
    intentOpenBluetoothSettings.setAction(android.provider.Settings.ACTION_BLUETOOTH_SETTINGS);
    startActivity(intentOpenBluetoothSettings);
  2. REQUEST_ENABLE_BT:
    http://www.cool3c.com/article/27452
    http://www.crifan.com/android_bluetooth_sample_code_can_not_found_request_enable_bt/
  3. BluetoothAdapter : http://developer.android.com/reference/android/bluetooth/BluetoothAdapter.html#ACTION_CONNECTION_STATE_CHANGED
  4. android BT: http://developer.android.com/guide/topics/connectivity/bluetooth.html#SettingUp
  5. Connected/Disconnected : http://stackoverflow.com/questions/19584423/how-to-check-if-bluetooth-connection-to-a-device-is-disconnected
[Connect]
[Profile]
  1. AVRCP (Audio/Video Remote Control Profile): http://www.techbang.com/posts/3050--avrcp-bluetooth-cell-phone-headset-is-so-controlled
    覺得用藍牙耳機控制音樂手機的上、下首、播放、停止和音量很有趣嗎？這是因為在藍牙技術協定中包含了AVRCP這個協定。它提供了搖控裝置一個標準的控制介面，讓你可以用一支遙控器或耳機等遙控裝置搖控你所有的電視、電腦或是手機的音訊和視訊介面
  2. webrtc : http://www.webrtc.org/reference/getting-started#TOC-Linux-Android-Specific-Steps