* .gitignore - don't ignore whole dirs and then opt-in specific files
* Makefile
- fail if required vars aren't set
- SCRIPTS --> ALL_SCRIPTS
* profiles/README.md
- variables.yaml --> vars.json
- drop 'not possible to add/modify/remove arbitrary files' comment
* make-amis
- use -eq for integer comparison
- make shellcheck happier with printf's
- remove old bad-idea TODO
* Build Profiles (completion of PR #49)
+ auto-updates version profile when new release detected
+ updates releases/<profile>.yaml after successful builds
* Prune AMIs (in AWS and in releases/<profile>.yaml
+ 'revision' - keep latest revision per release
+ 'release' - keep latest release per version
+ 'version' - remove end-of-life versions
* releases/README.md updater script
* README overhaul
+ Pre-built AMIs --> releases/README.md
+ profiles/README.md for profile configuration details
+ main README.md overhauled to go over how to build and manage custom AMIs
