box:

	* input
		writes content of data field to terminal

	* output
		enables passing of output to parent window (data field must be set
		to enable, disable or toggle)

	* session
		request sessions status

	* onsessionchange
		enables passing session status to parent window (data field must be
		set to enable, disable or toggle)

	* reconnect
		reconnects the terminal

	Following types of messages can be received from shellinabox:

	* ready
		signals that shellinabox is ready to send and receive messages