flatten the file hierarchy
correct a delimeter mistake in an original American Memory file
correct some obvious date transcription errors in the original American Memory files
simplify process_metadata.py --- we don't need to support round-tripping the three data formats
in JSON output, group neighboring rows together if they are multiple pages of the same bill
convert congress, session, and volume fields to int in JSON and remove leading zeroes in the CSV, and store dates in ISO format in both CSV and JSON
update the README
update bills.py and README