Adds VLC::Client::PlaylistControls#add_to_playlist
Adds VLC::Client::PlaylistControls#playlist
Adds VLC::Client::PlaylistControls#next and VLC::Client::PlaylistControls#previous
Adds VLC::Client::PlaylistControls#clear
Adds redcarpet for markdown
Moves VLC::Client::MediaControls#media_arg to VLC::Client#media_arg