Pyloan

Documentation has been further restructured and updated. Main changes allow to build the GitHub Page site for PyLoan in the /docs folder (for now the folder is populated with the ReadTheDocs template that contains PyLoan documentation).

Main changes include restructuring of the /docs folder, specifically:

- Documentation has been moved to /docs/docsrc folder in order to enable use of /docs for GitHub Pages.
- ReadTheDocs configuration file .readthedocs.yaml has been introduced. It points ReadTheDocs to /docs/docsrc/source/conf.py file for configurations.
- Sphinx method `make github` has been introduced in order to generate the documentation on the /docs/docsrc/build and then copy-paste it to /docs for GitHub Pages.

Enhance documentation, especially comparison between different day count methods and their impact on the total interest paid on a mortgage/loan over its term.