Openpaygo

What's Changed
* Unordered token entry by benmod in https://github.com/EnAccess/OpenPAYGO-Token/pull/5
* Python 2.7 compat by benmod in https://github.com/EnAccess/OpenPAYGO-Token/pull/6
* Updated README for v2.1 by benmod in https://github.com/EnAccess/OpenPAYGO-Token/pull/7

**Note:** This version is fully retro-compatible with the v2.0, the tokens themselves do not change. Changes can be implemented on devices that wish to support unordered token entry but are not required. No change is required on servers.

**Full Changelog**: https://github.com/EnAccess/OpenPAYGO-Token/compare/v2.0.0...v2.1.0

What's Changed
2019-10-10: v2.0 release

- Improved the test suite
- Added an extra example in the implementation documentation
- Bugfix in the example server implementation leading to count not always being updated correctly
- Bugfix in the update of count in the python device simulator

2019-09-27:

- Added signed independent security audit
- Added documentation as PDF

2019-09-06: v2.0 rc1

- Added extended token example implementation

2019-08-28: v2.0 beta

- Fully functional version with all v2.0 features

2019-07-19: v2.0 alpha

- First functional pre-release version


**Full Changelog**: https://github.com/EnAccess/OpenPAYGO-Token/commits/v2.0.0

New Contributors
* clema made their first contribution in https://github.com/EnAccess/OpenPAYGO-python/pull/16

**Full Changelog**: https://github.com/EnAccess/OpenPAYGO-python/compare/v0.5.4...v0.5.5

- Safe handling of datetime before UNIX timestamp minimum when generating answer timestamp

- Fix handling of `last_request_timestamp` when checking auth
- Updated PyPI doc

- Clarification in the doc of the behaviour when `secret_key` is missing
- Implemented coherent behaviour when `secret_key` is missing