Document API changes (manual approach)

[felipecruz91]

In this PR I've mainly kept the high-level documentation as it was. Then, I added warning messages about what methods are deprecated and what are the new ones that developers should use instead.

Finally, I decided to include a new section in the docs that will contain the Extensions API Reference. This is generated automatically with TypeDoc and it includes the TypeScript interfaces, their methods, params, return types, and examples that are documented in the source code of pinata.

I believe this is the sweet spot we're looking for: having a high-level documentation (tutorials, concepts, etc) and the API Reference that developers can use.

To learn more about how the API Reference is generated automatically, go to the pinata repo and check out the README of the extensions-preload module.

@technicallyjosh You can serve the documentation by cloning the repo and running:

docker run --rm -it -p 8000:8000 -v ${PWD}:/docs squidfunk/mkdocs-material

Visit http://localhost:8000