Add deep_reference_parser utilities

[ivyleavedtoadflax]

This is a long PR, but includes no new code. It is all just a move from datalabs, so please just skim if you are interested.

Moves utilities from the datalabs deep_reference_parser project to here. There utilities handle:

• Conversion from reach, spacy, prodigy, and tsv format.
• Conversion of manual reference annotations to token annotations in the IOBE schema.
• Rough annotation of numbered reference sections based on a deterministic splitting method.

Command line tools are accessible from:

$ python -m deep_reference_parser.prodigy                      
Using TensorFlow backend.

ℹ Available commands
annotate_numbered_refs, prodigy_to_tsv, reach_to_prodigy,
refs_to_token_annotations

Additional help is available with the --help flag for individual commands:

$ python -m deep_reference_parser.prodigy prodigy_to_tsv --help
Using TensorFlow backend.
usage: deep_reference_parser prodigy_to_tsv [-h] input_file output_file

    Convert token annotated jsonl to token annotated tsv ready for use in the
    Rodrigues model.
    

positional arguments:
  input_file   Path to jsonl file containing prodigy docs.
  output_file  Path to output tsv file.

optional arguments:
  -h, --help   show this help message and exit