Add devcontainer and update Hugo version

[ajschmidt8]

This PR adds a devcontainer to the repository.

A devcontainer makes it easier for others to contribute.

Additionally, it's a convenient prerequisite for migrating the main website to the Docsy theme, as mentioned in #334.

The Docsy theme has some additional dependencies (e.g. Golang, NodeJS, and some JS packages) that will be easier to track in a devcontainer.

The devcontainer has a start-up script that reads the HUGO_VERSION value from the netlify.toml value to ensure that the Hugo versions are consistent during local development and Netlify builds.

Other changes in this PR include:

• Updating the README to remove dead links, mention devcontainers, and other general clean up
• Migrating Hugo's config.toml file to a hugo.yaml file
• Updating Hugo to the latest version