Bert-extractive-summarizer

- Sentence separation was reverted, but now fixed. Test to ensure.

- Refactoring to make it easier for adding new transformer models.
- Bug fix: fixed issue with incorrect sentences.
- Fixed issue with spacing from sentences.
- Improved Doc strings.
- Cleaned up code with new proper naming and appropriate python packages.

In this version, a few minor fixes are added, along with the SBert implementation.

Paper: Sentence-BERT: Sentence Embeddings using Siamese BERT-Networks
Project: https://github.com/UKPLab/sentence-transformers

All features are available for SBERT that are available to the existing summarizer.

This release has Transformers 4 support.

This release contains two different features:

1. Elbow support. This includes returning inertias plus finding optimal cluster amount.
2. Optional return sentences as a list.