Weitersager

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- Recreated HTTP server as a WSGI application, built with Werkzeug and
served by wsgiref.

- Return status code 415 ("Unsupported Media Type") if request content
type is not ``application/json``.

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- Return status code 404 ("Not Found") on requests to any path other
than ``/``.

- Added Docker-specific configuration file example.

- Added configuration file for Docker Compose.

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- Changed application path in Docker container from ``/home/user`` to
``/app``. This is relevant when mounting the configuration file into the
container.

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- Added support for Python 3.10.

- Expect config file to be mounted into Docker container.

- Use non-inline array of tables for IRC channels in TOML configuration
examples.

- Reintroduce announcer as abstraction.

- Updated irc version to 20.0.0 (from 19.0.1).

- Updated rtoml to 0.7.1 (from 0.6.1).

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- Switched to using Python's logging mechanism directly, with different
log levels. Removed function ``util.log``.

- Made the application's log level configurable.

- Enabled threading for the HTTP server to reduce blocking.

- Introduced an internal queue to decouple reception of HTTP requests
from announcing messages on IRC.

- Added support for custom IRC commands to send after connecting
(authentication, cloaking, flood protection, etc.).

- Updated rtoml to 0.6.1 (from 0.5.0).

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- Added support for Python 3.9.

- Added support for SSL connections to IRC servers.

- Changed prefix of authorization header value from ``WTRSGR`` to less
awkward ``Token``.

- Removed handler to shut down Weitersager via private IRC message. It
doesn't provide enough relevant value.

- Added command line option ``--version`` to show Weitersager's version.

- Updated rtoml to 0.5.0 (from 0.4.0).

- Include tests and other useful files in source distribution archive.