Bert-extractive-summarizer

This release supports 3.0 for the sentence handler.

In this release, there are two new arguments for summarizer processing. One is the `hidden` parameter which now accepts an integer or a list. If supplied a list, it will combine the layers for the aggregation. Also, another parameter called `hidden_concat` allows the user to concat hidden layers before clustering.

Also a couple of new options for TransformerSummarizer.

In this release, two new reduce options are included: `concat_last_4` and `reduce_last_4`. The `concat_last_4` concats the last 4 BERT hidden layers and takes the mean for aggregation. The reduce last 4 option sums the last four layers and takes the mean across tokens.

Bug fixes.

Bert Extractive Summarizer now offers GPU support, if CUDA is available.