Antora refactor for HTML

[kersten1]

This PR creates the modules component for use with Antora (HTML). It also splits the 3 main profile adoc files into subcomponents to work better for HTML. Those components are put in specific subdirectories in src and the main adoc files are updated to pull them in. In theory, the PDFs should be identical to what is currently being generated.

If this is unacceptable, I can split the files in the modules directory and leave the files alone in src. However, then the HTML will not pick up updates unless they are manually copied in.

I also changed the links to the ISA manuals to work in the HTML. This action will likely break the PDF links. Again, I can revert this change if you wish - it was just exciting to link directly to the topic :)

Cheers!
Kersten

[aswaterman]

Krste's proposed document restructuring (https://lists.riscv.org/g/sig-documentation/message/691) has the profiles being moved into the ISA manual as Volume III. So I think we should hold off on Antora-ization of this repo, and instead do that as part of its integration into the ISA manual, which is in progress.