setup: prepare for ppypi upload
- revamp setup.pu a bit
- add build/ and dist/ in gitignore
related to swh-environment#1242 (closed)
Test Plan
https://test.pypi.org/project/swh-loader-core/
Migrated from D486 (view on Phabricator)
Staging instance, all changes can be removed at any time
related to swh-environment#1242 (closed)
https://test.pypi.org/project/swh-loader-core/
Migrated from D486 (view on Phabricator)