Pie-modules

:beetle: Fixes

* fix `RETextClassificationWithIndicesTaskModule` for `NaryRelation` (87) ArneBinder

:rocket: Features

* `NltkSentenceSplitter` returns the result document (85) ArneBinder
* add `NltkSentenceSplitter` (84) ArneBinder

:rocket: Features

* use multi span annotations and documents from PyTorch-IE (82) ArneBinder
* add task lr config for bart_as_pointer_network (81) jk-tripathy

:boom: Breaking Changes

* cleanup `PointerHead` logic regarding `decoder_position_id_mode` (79) ArneBinder
* remove parameter `span_layer_name` from `PointerNetworkTaskModuleForEnd2EndRE` (78) ArneBinder

:rocket: Features

* remove parameter `span_layer_name` from `PointerNetworkTaskModuleForEnd2EndRE` (78) ArneBinder

:rocket: Features

* implement `MultiSpanMerger` (76) ArneBinder
* add `RelationArgumentDistanceCollector` statistic (71) ArneBinder
* add token document types with multi spans (75) ArneBinder

:rocket: Features

* improve `RelationArgumentSorter` (73) ArneBinder
* adjust `trim_text_spans()` to work with `LabeledMultiSpan` (72) ArneBinder
* create `position_ids` based on a mapping (`PointerHead`) (67) ArneBinder
* add span utils (70) ArneBinder
* implement `SpanCoverageCollector` statistic (68) ArneBinder

:hammer: Refactoring

* make `utils` a package (69) ArneBinder