Clean up old files from JTD fork.

This PR would remove files from the Just-The-Docs fork which don't appear to be necessary for our site to function, including:

1. Old Docker/devcontainer files, which appear to have only been used for development of JTD.
2. Editor/tool-specific configuration files
3. The Just-The-Docs documentation markdown files.

This is the first step towards resolving #66 (closed), giving us a more solid base to start on. After this, we can move on to actual breaking changes.

merged

mentioned in commit a3b1d1ff