Enhacements to arXiv getter

[davidramsay95]

• paper_downloader():
  • GET requests to URL of a paper
  • Download .tar.gz file
  • Place downloaded file into appropriate folder (separate by year/month paper_id.tgz)
  • Keep a daily log in a text file (like logs/downloader/YYYYMMDD.log)
• add_to_database():
  • Keep the list of paper IDs that got downloaded at a given day to a text file YYYYMMDD.csv/txt
• call table_extractor():
  • Process the list of papers for a given day (based on the paper list csv/txt file)
  • As part of the extraction process, extract .tar.gz file into a tmp folder (we want to keep files compressed; just uncompress for extraction)