Clean up the IPlayer interface

[marijnz0r]

Clean up the IPlayer interface to be loosely coupled to the implementation. This opens up reusing the interface for usage in other implementations not coupled to the NAudio package.

[markjamesm]

Testing this PR, it seems that the pause button isn't working. After some review, it appears that lines 40-41 inside the Player method are creating a new instance of audioFileReader and outputDevice each time the Play button is pressed, which resets the pause method.

My solution was to move the initialization inside an if statement inside the Play method like so:

public void Play(string path)
{
if (this.outputDevice.PlaybackState == PlaybackState.Stopped)
{
this.audioFileReader = new AudioFileReader(path);
this.outputDevice.Init(this.audioFileReader);
}
this.outputDevice.Play();
}