New module to export the untagged_read/write functions about biniou

[mjambon]

It's a matter of performance (how to write say 4 bytes to a channel but perform only one bound check internally?), and also reusability (can't use channels for writing to string or to an arbitrary buffer).

Did you take a look at Bi_outbuf.create_channel_writer and Bi_inbuf.from_channel?

[UnixJunkie]

Bi_outbuf.create_channel_writer

Yes, I saw the make_room function can write to an output channel.

Wouldn't it be possible to use a functor to have the read/write_untagged_* functions
either work with a biniou in/out_buffer or an in/out channel?

I still think the read/write_untagged_* functions are useful even outside of biniou's context.
Pervasives from stdlib provides output_binary_int and input_binary_int but nothing
for floats for example.