FIX: fix m4 to search against python > 3.9 also

YAML updates and small bug fixes:

 -  add ymo_yaml_doc_get / ymo_yaml_doc_vget
 -  fix defaults if not set in config
 -  split WSGI config into header file (TEMPORARY HACK. Will tidy)
 -  reset optind after parse if we're going to parse more than once

TODO: Just discovered the yaml_document_t portion of the API in yaml.h.
Should migrate from ymo_yaml_doc_t to yaml_document_t.

Fix TLX Handshake and minor tweaks:

 - YAML: add some rudimentary yaml facilities to facilitate some
   file-based config
 - WSGI: implement websocket .close() method

Minor tweaks and fixes:

 - Fix PEP3333 compliance issues (SERVER_PORT and CONTENT_LENGTH should
   be strings, not ints)
 - Make UTF8 utilities available in public API
 - Add user data field to HTTP request wrapper
 - Tidy up header callbacks and Expect handling
 - Start tidying WSGI a little

Prerelease Alpha 10

0.1.0 PRERELEASE
================

API
---

 - Change response header "set" to "add" and "insert"
 - Add ymo_conn_send_buckets

Sketches (off by default)
-------------------------

 - TLS support (OpenSSL/WIP: don't use it).
 - Python WebSockets (Sketch)

Continuous Integration / Tests
------------------------------

All Push Events:

 - configure and make
 - run unit tests
 - test install
 - test docker image build
 - run HTTP server tests
 - run WS server tests
 - ensure that "make distcheck" passes

Tags:

 - create github release
 - add distribution tar.gz as a release asset
 - push yimmo-wsgi:<tag> docker image

Push to main:

 - push "latest" yimmo-wsgi docker image

Minor changes. Mostly docs, plus the following three things:

 - Websockets: provide user_data in callbacks + add set/get functions.
 - Core: fix misplaced ifdef that disabled nonblocking client FD's for
   systems without MSG_DONTWAIT
 - HTTP: split ymo_http_response_set_header -> *_add_header and
   *_insert_header

THE GREAT RE-SHUFFLING:

 - Move all src under "src"
 - Rename: lib->core; mod->protocol
 - Update headers to include dir prefix

Also:
 - Added user data functions for websockets sessions.
 - Move exchange refcount increment for wsgi_worker from http complete
   callback to http headers complete callback.
 - Fix the log message in ws_example.c!

BUGFIX: unbreak ws example.

Tidying, round one of a million:

  - Don't require config.h (ymo_config.h) in public includes
  - Generate yimmo.h from yimmo.h.in to inject version info + get rid of
    ymo_version_*()
  - Tidy up some unused vars
  - Address some compiler warnings (mostly fluff, but two pointer casts
    that were only not problematic by happenstance...)
  - Fix ABI ordering in configure.ac
  - Bump patch level / revision ahead of next update
  - Some docs updates (... and additional TODO items...)
  - Ensure ymo_config.h is the first thing included in source files
  - Add flexible array member hack to blalloc to work around lack of
  - Fix function pointer syntax in uncrustify (FIX: tell uncrustify to
    ignore from now on + fix by hand...)
  - Move ev callback typedef out of main docs...
  - Misc configure.ac fixes/tidying (...and more TODO items...)

Initial Public Release

Still lots in-flight. Marking public + pushing to work on integrating
repo-external tests into the repo + introduce some manner of CI.

In this release:

 - libyimmo: core I/O and utilities
 - libyimmo_http: HTTP 1.0/1.1 compliant
 - libyimmo_ws: RFC6455 compliant WebSockets
 - libyimmo_mqtt: Partial implementation of MQTT broker (stale)

Lots still TODO (see the README.md warning and/or the maintainer TODO
list for more info).

(No version bump for initial public release).