NOTE: A previous copy of this code was inadvertently merged and then
rolled back. This is the correct copy.

Chunked Encoding
================

Summary
-------
This commit implements both sending and receiving of Chunked-encoded
data according to https://datatracker.ietf.org/doc/html/rfc9112#section-7.1.

Receiving is done by implementing the hitherto unimplemented
`rdchnks^%ydbwebreq`.  This required some refactoring of other parts of
the routine. Tested by `tRecChuncked^%ydbwebtest` which calls
`/test/postchunked` (`chunkedpost^%ydbwebapi`).

`%ydbweburl` now supports a 4th data item. This can be anything, but now
we only support `chunkCallback=` will lets the POST url implement a
callback routine when each chunk is received.  URL `test/postchunkedinc`
sends each chunk through `chunkedpostincread^%ydbwebapi`, which puts it
in a variable `chunkedread`, and final processing is done in
`chunkedpostinc^%ydbwebapi`, which takes `chunkedread` and puts it in
`httprsp`. ...