Force data source files to be considered UTF-8

Fixes the error

    RuntimeError: Could not read content/libraries.md because the file is not valid US-ASCII.
Upgrade dependencies
Update the list of deprecated serialisation attributes

New additions:

- domain#private_whois?
- domain#parsed_expiration_date
- domain#expires_at
- contact#phone_ext
- user#first_name
- user#last_name