This fixes the case when webclient_set_static_body is used
for data larger than webclient_context::buflen.
Note: as of writing this, webclient_set_static_body is the
only user of body_callback in NuttX apps tree.
Highlights:
* TLS support (a hook to allow users to provide TLS implementation)
* ability to add extra request headers
* ability to use PUT method
* ability to report http status
* error handling improvements
Proposed on the ML while ago:
https://www.mail-archive.com/dev@nuttx.apache.org/msg03803.html
The original API is kept for now.
I plan to remove them after adapting the existing users.
(examples in this repo)
