Builder Overhaul

Subcommands

• merge 'resolve-profiles' and 'make-amis' into 'amis'
• rename 'update-releases' to 'release-yaml'
• rename 'gen-release-readme' to 'release-readme'
• rename 'prune-amis' to 'prune'
• reorder to match the usual workflow
• use argparse mutually-exclusive group where appropriate
• use argparse 'metavar' and 'nargs' for more salient help

ReleaseAMIs

• can now specify multiple AMIs on command line
• add explicit '--private' argument
• if no '--private', '--public', or '--allow-account' is specified, default to propagate the source AMI's permissions to its copies
• move 'iter_regions' and 'get*image' methods out of ReleaseAMIs class because they're also used elsewhere
• 'update_image_permissions' resets perms before adding new perms
• pending_copy loop, reports on everything in progress, waits 3m before reporting on everything again, and then waits 30s between reports
• pending_copy also notes when a copy has completed (and only queues for pending_perms if they need adjustment)

Releases class

• used by release-yaml and prune subcommands
• caches region client objects for later use (by prune)
• loads images from region - either from a profile or "unknown" (no profile tag)
• builds the releases object - now structured release -> build (instead of build -> release)

ReleasesReadme

• works with new releases object format
• improve sorting and selection of latest per version per-build AMIs
• empty cell if a region doesn't happen to have a build AMI there

PruneAMIs

• rename 'version' level to 'end-of-life'
• add 'UNKNOWN' pruning level
• works, even if you don't want to --use-broker
• --keep N - keeps an additional N AMIs that would otherwise have been purged per build
• --defer-eol DAYS - give EOL AMIs a grace period past their official EOL date
• no AMI deletion happens unless --no-pretend arg is provided
• improve pruning criteria scan and candidate selection

resolves #102 (closed)

Also includes updated releases/README.md and releases/alpine.yaml.