htx_xfer() function should replace htx_xfer_blks(). It will be a bit easier to
maintain and to use. The behavior of htx_xfer() can be changed by calling it
with specific flags:
* HTX_XFER_KEEP_SRC_BLKS: Blocks from the source message are just copied
* HTX_XFER_PARTIAL_HDRS_COPY: It is allowed to partially xfer headers or trailers
* HTX_XFER_HDRS_ONLY: only headers are xferred
By default (HTX_XFER_DEFAULT or 0), all blocks from the source message are moved
into to the destination mesage. So copied in the destination messageand removed
from the source message.
The caller must still define the maximum amount of data (including meta-data)
that can be xferred.
It is no longer necessary to specify a block type to stop the copy. Most of
time, with htx_xfer_blks(), this parameter was set to HTX_BLK_UNUSED. And
otherwise it was only specified to transfer headers.
It is important to not that the caller is responsible to verify the original
HTX message is well-formated. Especially, it must be sure headers part and
trailers part are complete (finished by EOH/EOT block).
For now, htx_xfer_blks() is not removed for compatiblity reason. But it is
deprecated.
It's not always easy to figure that there are some docs on internal API
stuff, let's move them to their own directory. There's a diagram for
lists that could be placed there but instead would deserve a greppable
description for quick lookups, so it was not moved there.
