Delft

- fix serialization of models with feature preprocessor (PR 110)
- update grobid models with features
- some other models and score updates
- add "software was used" classification model for software citations
- update tensorflow dependency

- generic support for feature channel in sequence labeling, test with Grobid training data
- fix issues 40 44 48 50 52 54 56 66 69 71 94 100 103
- update eval (average field level n-fold cross-validation)
- dataseer and software use classification models
- review and improvement for BERT sequence labeling and classification (unicode, binary/multi-label, test SciBERT, bioBERT, ...)
- force split lemonde corpus evaluation (to be compared with some publication results using this)
- fixing truncation in sequence labeling
- more documentation
- various bug fixing