Python API for Yi 4k camera.

It is based on official Yi 4k Java API.
Differences from original API:

• Commands are blocking waiting for result, while in original API they return promices.
• 'stopRecording' and 'capturePhoto' waits till operation is really ended and return produced file name.
• Values provided to commands should be correct strings, compared to integers in original API.
• 'adapter', 'adapter_status' and 'battery_status' callbacks are available in addition to all other. .setCB() used to set/get callbacks.
• 'deleteFile' and 'getFileList' commands require path relative to DCIM folder.

Try not to call same commands simultaneously from different threads: camera response is not clearly identified with caller and response can be mixed.

###Commands not implemented:

• formatSDCard
  NSFW

• downloadFile

• cancelDownload
  Redundant, available by http

• getRtspURL
  Redundant, available at YiAPI() creation

• buildLiveVideoQRCode
  Maybe later

• startRecording datetime
  Lazy to implement due to specific input value format