Batch processing

[pszemraj]

this PR contains some more behind-the-scenes improvements related to ease-of-use and/or batch processing for the Summarizer class object:

• disable the progress bar for within-loop summarization of a single long string
• add a 'smart' __call__ function that hands off to the text and filepath processing fns
• small improvements/updates to docs

[pszemraj]

todo:

• check/test that the default-disabled autocast doesnt break anything
• add a batch_delimiter (or similar) kwarg for setting the join string for output of summarize_string()