Document deployment to github.io

[dbenn]

We have recently deployed Javadoc for latest stable and snapshot tags via https://github.com/AAVSO/VStar/blob/master/.github/workflows/javadoc.yml

All other documentation should be deployed for latest stable and snapshot releases:

• User manual
• Plugin development doc
• All plugin docs

The base URL (urlStr) in openPluginHelp() will have to change to the new location.

The user manual link here will have to change: https://www.aavso.org/vstar

A nice benefit will be that PDF files will open in the browser properly, not in a GitHub page.

[dbenn]

At formal release time, and of course after the PR merges and a successful workflow run, the user manual link on https://www.aavso.org/vstar can be updated on the AAVSO website.