Add Tweet LogicalType (or semantic tag)

- As a user, I wish I could indicate that certain columns contain tweets, as there are certain primitives being proposed (https://github.com/alteryx/nlp_primitives/issues/140 and https://github.com/alteryx/nlp_primitives/issues/139) that are really meant to be used on tweets, and not normal natural language columns.

This logical type would be a sub-type of NaturalLanguage, and it has certain properties that could be used for validation or inference (mostly that they are less than 240 characters and contain natural language).

If we don't want to make this a logical type, we could just use semantic tags and add `tweet` or something as one of the known semantic tags in the types and tags guide.