Pie-datasets

* upgrade `pytorch-ie` to 0.28 (38) ArneBinder
* create core package (37) ArneBinder
* remove some statistics (35) ArneBinder
* add statistics (29) ArneBinder
* integrate `Dataset` related classes from PyTorch-IE (21) ArneBinder

:tada: New Dataset

* add generic `brat` dataset (12) ArneBinder

:beetle: Fixes

* remove leftovers from datasets in pytorch-ie (31) ArneBinder

:construction_worker: Continuous Integration

* do not assert minimum test coverage via pytest (30) ArneBinder

:tada: New Dataset

* add conll2003 dataset (14) ArneBinder

:rocket: Features

* implement `TextSpanTrimmer` (20) ArneBinder
* implement `RegexPartitioner` (19) ArneBinder

:beetle: Fixes

* add "Document Converters" section to conll2003 dataset card (17) ArneBinder
* fix importing all modules in conftest.py (16) ArneBinder
* fix coverage score (and report) for unused source files (11) ArneBinder
* fix codecov upload (8) ArneBinder

:rotating_light: Testing

* codecov ci: set target to 90% for the patch job (25) ArneBinder
* add codecov threshold (24) ArneBinder
* add `codecov.yml` to set target coverage to 90% (23) ArneBinder

:construction_worker: Continuous Integration

* codecov ci: set target to 90% for the patch job (25) ArneBinder
* add codecov threshold (24) ArneBinder
* add `codecov.yml` to set target coverage to 90% (23) ArneBinder

* add "New Dataset" section to release (5) ArneBinder

:tada: New Dataset

* add TACRED dataset (1) ArneBinder

* add link to pie namespace on HF to readme (3) ArneBinder