Packageurl-python

----------------------

- Fixed `PackageURL.from_string` to properly handle npm purls with namespace.

-------------------

- Refactor the purl2url functions and utilities 42

- Split purl2url into `get_repo_url()` and `get_download_url()` returning
accordingly a "Repository URL" and a "Download URL".
- A new `get_inferred_urls` function is available to get return all
inferred URLs (repository and download) values.
- Add support in purl2url for npm, pypi, hackage, and nuget.
- Package URL qualifiers can now be provided to `purl_from_pattern()`.
- The `download_url` qualifier is returned in `get_download_url()` when available.

- Usage of `purl2url.purl2url` and `purl2url.get_url` is still available for
backward compatibility but should be migrated to `purl2url.get_repo_url`.

- Include the `version_prefix` ("v" or "V") as a qualifier in build_github_purl 42
This allow to infer valid URLs in the context of purl2url.

-------------------

- Fix named arguments in purl_to_lookups.

-------------------

- Add encode option in purl_lookups 94
(`purl_to_lookups`, `without_empty_values` is moved from packageurl.contrib.django.models
to packageurl.contrib.django.utils)

-------------------

- Add ability to filter objects with EMPTY purls in PackageURLFilter 92

-------------------

- Upgrade virtualenv.pyz to latest version 85
- Replace Travis CI by GitHub Actions 84
- Add black to the CI and apply formatting on whole codebase 91
- Improve url2purl support for nom URLs
- Improve url2purl support for rubygems.org URLs 89