Update to Python 3

[adelavega]

This PR is a major update to Python 3, and updates most of the scraping code to work as of March, 2023

I also added the following changes

• Can add a PubMed API Key
• Can specify a maximum pubmed id
  • Refactor PubMed API code to use XML and have generic class to handle requests

In addition, this PR fixes a few issues with exporting, including adding text, and issues in NV scraping