Fixed missing mapped_topics

When transforming new documents, self.mapped_topics seemed to be missing. Added to the init.

Fixed requirements

• Fixed requirements --> Issue with pytorch
• Update docs
• Update readme

First Release

• Added parameters for UMAP and HDBSCAN
• Option to choose sentence-transformer model
• Method for transforming unseen documents
• Save and load trained models (UMAP and HDBSCAN)
• Extract topics and their sizes
• Optimized c-TF-IDF
• Improved documentation
• Improved topic reduction