type page = (((unit -> string Ocsigen_stream.t Lwt.t) list) *
Allows to send raw data using Ocsigen's streams.
The content is a pair conatining:
- a list of functions returning a stream and the function to close it,
- the content type string to send.
Streams are opened by calling the functions in the list, and closed
automatically by a call to the closing function.
If something goes wrong, the current stream is closed,
and the following are not opened.