Add Language Model Decoder

dan/datasets/extract/extract.py

dan/datasets/extract/utils.py

dan/ocr/decoder.py

dan/ocr/predict/__init__.py

dan/ocr/predict/prediction.py

dan/utils.py

docs/get_started/training.md

docs/usage/datasets/extract.md

docs/usage/index.md

docs/usage/predict/examples.md

docs/usage/predict/index.md

docs/usage/predict/parameters.md

docs/usage/predict/training_lm.md

mkdocs.yml

requirements.txt

tests/data/prediction/language_lexicon.txt

tests/data/prediction/language_model.arpa

tests/data/prediction/language_tokens.txt

tests/data/prediction/parameters.yml

tests/test_extract.py