Include Common Metadata Tasks

[OliverSherouse]

Probably add in a metadata module. At the very least, include word counting and the ability to count occurrences of specific words and phrases.

[OliverSherouse]

• word counting
• shannon entropy
• conditional counts
• sentence length (via spaCy?)

[mgasvoda]

I'm going to separate this out into separate issues so we can work on these in smaller chunks