Update mkdocs to use mkdocs-material and update structure

[theskumar]

Why was this change necessary?

For better documentation structure and design.

How does it address the problem?

• Update the mkdocs to use mkdocs-material theme.
• The endpoint.md is now broken into per resource files.
• The api/changelog.md is removed and it's advised to use release_notes.md in it's place.
• The index.md will now include the release_notes as well, included via markdown-include, in order to make the doc homepage more meaningful.
• Writing of docs is improved using a lot of markdown extensions. Do check them out.

Are there any side effects?

User used to old structure may face issue to due the new structure.