* Create RELEASE_NOTES.md for tagged releases too
Required to publish notes for the Base version.
Additional Makefile comments and a 'help' target too.
* Fix header level in pvaClient release notes
* Prevent parallel builds in documentation
* Restores inclusion of old notes, works without git
- Use a Sphinx/Myst {include} directive to pull the text from all previous
RELEASE files into the output, which makes the website sidebar index work
properly.
- Exclude the RELEASE files from the files given to RTD to publish, they
aren't needed now and generate warnings if included.
- Updated the intro paragraph in all RELEASE files.
Adds new-notes files for the PRs already merged.
Future conflicts in the now-deleted RELEASE_NOTES.md file must be
turned into new-notes/PR-nnn.md files when resolving them.
Andrew Johnson