Datasette-scale-to-zero

- Loosened validation requirements for `"shutdown_url"` to support configuring it via an environment variable that might be blank. [7](https://github.com/simonw/datasette-scale-to-zero/issues/7)

- New mechanism for optionally sending an HTTP request when the server shuts down, controlled by the configuration options `shutdown_url` and `shutdown_method` and `shutdown_headers` and `shutdown_body`. [5](https://github.com/simonw/datasette-scale-to-zero/issues/5)
- Renamed `max-age` to `max_age` (though the old name still works). [6](https://github.com/simonw/datasette-scale-to-zero/issues/6)

- New `"max-age": "10h"` configuration setting, which causes the server to exit after the specified amount of time whether or not it has received any traffic. [3](https://github.com/simonw/datasette-scale-to-zero/issues/3)

- No longer logs a traceback on server exit. [2](https://github.com/simonw/datasette-scale-to-zero/issues/2)

- Reduced log output when server exits. [2](https://github.com/simonw/datasette-scale-to-zero/issues/2)

- Initial release. Can be configured to cause Datasette to exit if it has not received traffic in a specified time period. [1](https://github.com/simonw/datasette-scale-to-zero/issues/1)