Mastercard-oauth1-signer

- Added compatibility with client code generated using OpenAPI Generator version [5.2.1](https://github.com/OpenAPITools/openapi-generator/releases/tag/v5.2.1)

- Fixed issue https://github.com/Mastercard/oauth1-signer-python/issues/35: `oauth_signature` not encoded in versions **1.2.0** and **1.3.0**
- Fixed security hotspot [python:S2245](https://rules.sonarsource.com/python/RSPEC-2245)
- Keep the behavior consistent with other [Mastercard OAuth1.0a signer libraries](https://github.com/Mastercard?q=oauth1-signer&type=&language=&sort=) when encoding URL and params
- The `OAuth1RSA` module reuse the core functions instead of redefining them
- `sha256_encode`: added support for `byte` payload
- Moved `nonce` and `timestamp` generation function into the utils module
- `get_authorization_header` method is now static in `OAuth` class
- Added [pycodestyle](https://pypi.org/project/pycodestyle/) GitHub workflow and fixed sonar scan not running on new Pull Requests
- Improved code coverage

* Added support for list payloads

- Added `oauth_ext` authentication extension for simplifying the requests signing process (https://github.com/Mastercard/oauth1-signer-python/issues/19)
- Removed unnecessary RFC 3986 encoding of the Authorization header
- Removed cryptography lib dependency

* Fixed 2 ("If the request does not have an entity body, the hash should be taken over the empty string")
* Removed unused 'self' param from static functions

* Fixed `requirements.txt` with missing dependencies
* Removed unused dependencies from `setup.py`
* Updated `README.md`
* General clean-up
* Added Python 3.8-dev to the Travis CI environments