generate release notes via script

[leonstafford]

have the scripts already to generate the environmental info, wrap this in another script to generate the markdown with collapsible sections and a placeholder for features/changes. Can auto-insert the release version into title, etc, for easy copying into GitHub releases page.

If want to get smarter, can write the release notes under correct version number in CHANGELOG.md and have it parse and include that. Yes, that sounds wiser, forces me to update the CHANGELOG!