v0.3.0: duckdb support, prepare for sql win_over

What's Changed

• feat: add duckdb as a SQL backend by @machow in #422
  • breaking: LazyTbl still takes a sqlalchemy Engine, but can no longer take a sqlalchemy Connection.
• feat: allow head() over grouped data by @machow in #420
• docs: update import for plotnine example by @isabelizimm in #421
• ci: add wheel build to release by @machow in #423
• refactor: prepare for sql win_over by cleaning up sql Over clause code @machow in #412

New Contributors

• @isabelizimm made their first contribution in #421

Full Changelog: v0.2.3...v0.3.0