This class provides an interface for managing VPN connection. A basic workflow looks as follows:
1. Call prepare() method to establish connection to VPN Unlimited service or creates a new one.
2. Configure VPN server item using setup(com.keepsolid.androidkeepsolidcommon.vpnunlimitedsdk.entities.VPNUServer, com.keepsolid.androidkeepsolidcommon.vpnunlimitedsdk.entities.VPNUProtoConfig, boolean) method.
3. Add OpenVpnStatusChangedListener for observing connection status.
3. Connect to the configured VPN server using startVpn() method.
4. Disconnect at any time using stopVpn() method.
Before using this class you must authorize or register with the help of KSAuthorizer class.
You must pass the same KSAuthorizer instance to its constructor as you have passed to KSAuthorizer instance constructor.