def add(channel, client)
      @lock.synchronize do
        _remove(client) if @clients.include? client and @clients[client] != channel
        debug { "Adding #{client} to #{channel}." }
        @clients[client] = channel
        @channels[channel] = @channels[channel] ? @channels[channel] + 1 : 1
      end
    end
def add(channel, client)
      @lock.synchronize do
        _remove(client) if @clients.include? client and @clients[client] != channel
        debug { "Adding #{client} to #{channel}." }
        @clients[client] = channel
        @channels[channel] = @channels[channel] ? @channels[channel] + 1 : 1
      end
    end
Creates a new registry.
 Registers a new client for that channel. Migrates client to new channel
 if client already exists.
 @param [String] channel ID
 @param [String] client ID