livedigital SDK usage

See Integration for integration instructions. Further steps assume you have successfully integrated the SDK and host application project can be built as normally.
Choose or create a class in your app that will be the main livedigital services client. Let’s call it LivedigitalClient.
In the beginning of LivedigitalClient.swift file, import the SDK module:
```
 import LiveDigitalSDK
```

Create an instance of the livedigital services engine and store it as a property in your client class:

     private let engine: LiveDigitalEngine
     private var channelSession: ChannelSession?
     private var videoSource: VideoSource?
     private var audioSource: AudioSource?

     init() {
         let creds = AppCredentials(
                 id: "put_your_app_id_here",
                 secret: "put_your_app_secret_here")
         self.engine = StockLiveDigitalEngine(appCredentials: creds)
     }
 }

Implement engine’s and session’s delegate protocols to handle appropriate events:

 extension LivedigitalClient: LiveDigitalEngineDelegate { ... }
 extension LivedigitalClient: ChannelSessionDelegate { ... }

To see other peers in channel, your app should handle next events and take care of displaying peer video views:

 func peerJoined(_ peer: Peer) {
     // Show peer as an active member of channel.
 }

 func peerDisconnected(_ peerId: PeerId) {
     // Hide peer from active members list/.
 }

 func peerAddedVideoView(peer: Peer, videoView: UIView) {
     // Display and layout the `videoView`.
     // This view will render video stream that `peer` broadcasts.
 }

Prepare for microphone and camera usage. AppInfo.plist file must include non-empty values for NSMicrophoneUsageDescription and NSCameraUsageDescription keys. Your app is responsible for requesting user permissions to use microphone and camera. You may use next calls to show system requests:
```
 AVAudioSession.sharedInstance().requestRecordPermission { ... }
 AVCaptureDevice.requestAccess(for: .video) { ... }
```
Next steps assume that user has granted microphone and camera permissions.

Join to a channel by starting channel session and becoming its delegate:

 let channelId = ChannelId(value: "put_your_channel_id_here")
 let channelSession = engine.connectToChannel(channelId)
 channelSession.delegate = self
 self.channelSession = channelSession

Start broadcasting audio and video to the channel:

 let videoSource = engine.startVideoSource()
 session.addVideoSource(videoSource)
 self.videoSource = videoSource
	
 // Display `videoSource.localVideoView`
 // somewhere to show camera preview.
	
 let audioSource = engine.startAudioSource()
 session.addAudioSource(audioSource)
 self.audioSource = audioSource

You will need at least two separate devices to test audio/video conferences appropriately. But for more convenient debug process, you may use next flag to make quick tests with just a single device:
```
 channelSession.shouldShowLocalPeer = true
```