minor metadata edits

• change author name to Zyte
• add readme to pypi

replace bsddb3 with Python's dbm for storing request fingerprints

• drop Python 2 support
• replace bsddb3 with Python's dbm for storing request fingerprints
• minor README fix
• option to disable deltafetch for some requests with deltafetch_enabled=False request meta key
• dev workflow: changed from Travis to Github Actions