* .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
* Match meanings of 'version' and 'release' to how Alpine uses them
* Use optional 'revision' to denote any same-release AMI rebuild
* Include CPU 'arch' in naming/description (may also offer 'aarch64' AMIs someday)
* Upgrade build instance to use Amazon Linux 2 AMIs
* Use env vars to pass details to 'make_ami.sh' instead of via CLI parameters
* make_ami.sh
+ minimum version/release shouldn't be overrideable
+ update APK tools & Alpine keys
+ check build's release vs. installed /etc/alpine-release
* standardize on 'linux-virt' kernel
+ no longer need 'kernel_flavor' variable
+ always install 'aws-ena-driver' package
+ always enable ena_support
* switch to 'variables.yaml' for config
+ update build/convert script to stringify certain keys that may contain arrays
+ copy from 'variables.yaml-default' if it doesn't exist
* drop 'vpc' variable, using 'subnet' derives the proper VPC to use
* fix chrony.conf (all pool.ntp.org references are changed to 169.254.169.123)
* update README.md caveats
