Opentabulate

Added

- Multi-threading support to allow parallelized processing of input data
- Caching using hash digests to avoid redundant data processing when invoking OpenTabulate more than once

Changed
- Improved error and logging messages
- Reorganized package contents n a code base, additional package data and unit tests
- Completed basic unit tests for `algorithm.py`

This release of OpenTabulate is an overhaul of the earlier version to make it more simple and flexible. Several features have been added and removed.

Added

- [Design specification](https://opentabulate.readthedocs.io/en/stable/source/design.html)
- [Project changelog](https://opentabulate.readthedocs.io/en/stable/source/changelog.html)
- [Configuration file](https://opentabulate.readthedocs.io/en/stable/source/configuration.html) with processing and output schema configuration

Changed

- Refactored code (renamed variables, relocated classes into files, removal of redundant code, implemented new functions)
- Ported Markdown documentation to ReST/Sphinx, now hosted [here](https://opentabulate.readthedocs.io/en/stable/)

Removed

- ZIP file handling
- Address parsing