Support for Python 3.9 with Docker

[ x] Testing with python 3.9
[ x] Integration with docker
[ x] Setup.py file fix
[ x] Deploy with Pip API token
[ x] Documentation update

Multiple date format support

• [ x] setup.py file fix
• [ x] Documentation

Support python 3.8

Code refactoring
Fix for RFC calculation.
Implementation of the divmod method.
String Format.
Support python 3.6
Support python 3.8
+

What's Changed

• Fix residuo conditions by @GMakarenko in #7
• Elimination of constant file and implementation of string format. by @thomgonzalez in #8
• Setup file updated. by @thomgonzalez in #9
• updated setup file v2. by @thomgonzalez in #10

New Contributors

• @GMakarenko made their first contribution in #7
• @thomgonzalez made their first contribution in #8

Full Changelog: v1.2.1...v2.0