Proxpi

*Changes since v1.0.1*

Fixes
* Don't provide `data-dist-info-metadata` attribute (from [PEP 658](https://peps.python.org/pep-0658/)), see #23

*Changes since v1.0*

Fixes
* Relative files for URLs from source index servers are joined with their package's request base URL to make them absolute for downloading
* Support package index responses with no HTML body element
* Provide package only found in extra indexes instead of 404

Improvements
* Add `proxpi` user-agent to requests to package indexes
* Request HTML from package indexes

Miscellaneous
* Constrain dependency versions

*Changes since v1.0.1rc1*

Fixes
* Support package index responses with no HTML body element
* Provide package only found in extra indexes instead of 404

Improvements
* Add `proxpi` user-agent to requests to package indexes
* Request HTML from package indexes

Miscellaneous
* Constrain dependency versions

*Changes since v1.0*

Fixes
* Relative files for URLs from source index servers are joined with their package's request base URL to make them absolute for downloading

*Changes since v0.1*

Features
* Add home page with index invalidation and link to index root
* Add environment variable `PROXPI_CACHE_DIR` to set file-cache directory

Changes
* Use [Gunicorn](https://gunicorn.org/) for serving in Docker container

Improvements
* Reduced Docker image size
* Avoid requesting index by assuming package URL
* Use single request session for cache
* Protect file-cache eviction with a lock
* Remove smallest files first when evict from file-cache
* Convert user-assert into RuntimeError
* (Attempt to) log `proxpi` version on server start-up

Fixes
* Download-fail response not cached