* make it easier to switch between bootloaders
* experimental (non-working) EFI_STUB bootloader
* remove apk_tools & alpine_keys from profiles
* determine & install appropriate apk_toosl & alpine_keys in setup-ami based on version and arch.
release alpine-ami-3.12.1-aarch64-r1
Also...
* release new edge builds
* Alpine 3.9 is EOL
* build_instance_type set in profiles/arch/
* a couple comment fixes
* eth-eni-setup init script
before networking starts up, makes sure eth interfaces match attached ENIs
also fixes a permissions problem with eth-eni-hotplug mdev config
* fix aarch64 build
* 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
