Change the `XCDMoviePlayerPlaybackDidFinishErrorUserInfoKey` constant

Use @"error" instead of @"XCDMoviePlayerPlaybackDidFinishErrorUserInfoKey" for interoperability with MPMoviePlayerController.
Add hyperlink to the LICENSE file
Also parse the `adaptive_fmts` key

In order to be ready for either
  1. YouTube support of HTTP Live Streaming  (HLS)
  2. iOS support of Dynamic Adaptive Streaming over HTTP (MPEG-DASH)
Set code indentation settings to 4 tabs
Demonstrate how to play a video in background
Enable arm64
Try to ensure that the medium thumbnail URL is always available
Fill the “Now Playing Info Center” with available metadata
Add screenshot, social media URL and license file in podspec
Save the audio session category in user defaults
Fix AVFoundation.framework and MediaPlayer.framework paths