Add API doc website

[bact]

• Add API doc build workflow
• Fix <text> </text> in Javadoc, it has to be escaped
• Fix few other Javadoc
• Convert @author to SPDX-FileContributor

Demo: https://bact.github.io/spdx-java-tagvalue-store/

(Note: a Pages settings to point to gh-pages branch is needed after merge + CI run)

[goneall]

Let's leave the original notice texts in the source file since it is recommended by the Apache software foundation: https://www.apache.org/legal/apply-license.html

The other changes is to keep Java 8 compliance - last time I tried to change that, I got complaints from the user community that their company is still using Java 8.

[goneall]

@bact - If you could rebase to the latest, it should fix the CI failure

[goneall]

Since I would like to get a release out today and this change is mostly documentation, I'll include it in the the next release after 2.0.0-RC2

[bact]

Let's leave the original notice texts in the source file since it is recommended by the Apache software foundation: https://www.apache.org/legal/apply-license.html

@goneall I have add back the short license header as suggested.

Note that the guideline you have mentioned is probably for the code that is developed at the Apache Software Foundation.

From https://www.apache.org/legal/apply-license.html - there's a link to the short license header at https://www.apache.org/legal/src-headers.html#headers and it said:

"Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership"

and the NOTICE file https://www.apache.org/legal/src-headers.html#notice said:

"Apache [PRODUCT_NAME] Copyright [XXXX-XXXX] The Apache Software Foundation This product includes software developed at. The Apache Software Foundation (/)."

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Btw, for the URL changes, the guideline also said:

"https is acceptable in place of http for the URL"