scripts/builder.py...
GenReleaseReadme:
* combine with ReleaseReadmeUpdater
* generates README_<profile>.md
* README_alpine.md is a symlink to README.md
* don't crash when README doesn't preexist
* append image list to README if no list found to replace
MakeAMIs:
* collect all artifact IDs and report after all builds
* don't update releases/readme
PruneAMIs:
* defaults to pretend mode, unless --no-pretend
* improve readability
UpdateReleases:
* replace code with what was RefreshReleases