Setup automatic publishing of AsciiDoc documentation and Javadoc

[janbeernink]

Please set up a GitHub action to automatically publish documentation to the gh-pages branch.

For any new tag, in the gh-pages branch:

• Create a new directory named 'docs/tag', where tag is the name of the tag.
• Copy the generated AsciiDoc to 'docs/tag'.
• Copy the generated Javadoc to 'docs/tag/javadoc'.

For any new commit in the develop branch, do the following:

• Create a new directory named 'docs/snapshot', where snapshot is the snapshot version.
• Copy the generated AsciiDoc to 'docs/snapshot'.
• Copy the generated Javadoc to 'docs/snapshot/javadoc'.