docs: browsable API reference on GitHub Pages

[uniqueg]

• Add docstrings to all public modules, classes, methods and functions
• Build markdown documents of all module, class, method and function docstrings with lazydocs
• Move detailed docs with notes and recipes to /docs directory, together with API reference
• Build and publish contents of /docs directory with MkDocs on GitHub Pages
• Add CI workflow to automatically build and publish docs when code changes are pushed on branch master

Resolves #9

NOTE: PR is ready to review, but not ready to be merged. First, GitHub Pages have to be enabled for this repository.
Afterwards, there may be some minor changes required to initalize the docs deployment.

Screenshots

Screenshots are from local build:

Docs landing page

API reference overview

tes.client

tes.models

tes.utils