Allow users to override NER with known locations

[ahalterman]

Sometimes the spaCy NER step fails with very short documents, including examples where the entire document is just a single sentence, because it's lacking the usual context to identify locations. This happens especially with locations outside of Europe or English-speaking countries because of the limitations of the NER training data.

It would be nice to allow users to override the NER step and force a geolocation on a known entity.

The easiest way to do this would probably be to:

• pull most of the geolocation logic out of geoparse_doc into a separate function
• create a new function (geoparse_ent?) that takes a document + entity string as arguments. It can then manually add the string entity as a spaCy entity, and then call the new function above.