Fugue

- [Extension validation](https://github.com/fugue-project/fugue/issues/81) interface and interfaceless syntax
- Passing dataframes cross workflow ([yield](https://github.com/fugue-project/fugue/pull/94))
- [OUT TRANSFORM](https://github.com/fugue-project/fugue/issues/82) to transform and finish a branch of execution
- Fixed a PandasDataFrame datetime [issue](https://github.com/fugue-project/triad/issues/59) that only happened in transformer interface approach

- Unified checkpoints and persist
- Drop columns and na implementations in both programming and sql interfaces
- Presort takes array as input
- Fixed jinja template rendering issue
- Fixed path format detection bug

- Require pandas 1.0 because of parquet schema
- Improved Fugue SQL extension parsing logic
- Doc for contributors to setup their environment

- Added set operations to programming interface: `union`, `subtract`, `intersect`
- Added `distinct` to programming interface
- Ensured partitioning follows SQL convention: groups with null keys are NOT removed
- Switched `join`, `union`, `subtract`, `intersect`, `distinct` to QPD implementations, so they follow SQL convention
- Set operations in Fugue SQL can directly operate on Fugue statemens (e.g. `TRANSFORM USING t1 UNION TRANSFORM USING t2`)
- Fixed bugs
- Added onboarding document for contributors

<=0.4.0

- Main features of Fugue core and Fugue SQL
- Support backends: Pandas, Spark and Dask

* Add version cap for jupyter-lsp

* Upgrade to Fugue 0.8.0