WIP: [DOCS] Add documentation

[mr-ubik]

• Document all the Solidity code <3
• Use solidity-docgen to extract NatSpec as .md files
• Use mkdocsto generate the docs

[mr-ubik]

Even though we are currently using a "working" documentation generation pipeline, it's held together with ducktape and prayers. This PR won't be considered complete until a proper documentation framework is either found or developed.