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.

.devcontainer/Dockerfile

-# [Choice] Debian OS version (use bullseye on local arm64/Apple Silicon): bullseye, buster
-ARG VARIANT=bullseye
-FROM mcr.microsoft.com/vscode/devcontainers/jekyll:0-${VARIANT}
-
-# [Choice] Node.js version: none, lts/*, 16, 14, 12, 10
-ARG NODE_VERSION="none"
-RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"; fi
-
-# [Optional] Uncomment this section to install additional OS packages.
-# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
-#     && apt-get -y install --no-install-recommends <your-package-list-here>
-
-# [Optional] Uncomment this line to install global node packages.
-# RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && npm install -g <your-package-here>" 2>&1
\ No newline at end of file