Frictionless

- Improved checks/steps API (621) (BREAKING)
- Updated `validate(extra_checks=[...])` to `validate(checks=[{"code": 'code', ...}])`

- Updated describe/extract/transform/validate APIs (BREAKING)
- Removed `validate_table` (use `validate_resource`)
- Removed legacy `Table` and `File` classes
- Removed `dataflows` plugin
- Replaced `nopool` by `parallel` (not parallel by default)
- Renamed `report.tables` to `report.tasks`
- Rebased on `report.tasks[].resource` (instead of plain path/scheme/format/etc)
- Flatten Pipeline steps signature

- Introduced Layout class (BREAKING)
- Renamed `Query` class and arguments/properties to `Layout`
- Moved `header` options from `Dialect` to `Layout`

- Updated transform API
- Added `transform(type)` argument

- Updated describe API (BREAKING)
- Renamed `describe(source_type)` argument to `type`

- Updated extract API (BREAKING)
- Removed `extract_table` (use `extract_resource` with the same API)
- Renamed `extract(source_type)` argument to `type`