Update documentation and release 3.0.1

[zaneselvans]

Changes that need to be documented:

• Note: now requires Python 3.6+
• New non-string path DBF access: filedata + memofile/ignore missing memo args and ignored path arg.
• Check / update check README.rst & changes.rst
• Create examples of access without string path, including access within a zip archive
• Get docs building at https://catalystcoop-dbfread.readthedocs.io
• tag and release v3.0.1