Migrated from github.com/containerd/containerd/plugin

What's Changed

• Add repository files by @dmcgowan in #1
• Cleanup plugin interface by @dmcgowan in #2
• dynamic: expose count of loaded plugins by @samuelkarp in #3
• Properly handle skipped plugins in plugin get by @dmcgowan in #4

New Contributors

• @dmcgowan made their first contribution in #1
• @samuelkarp made their first contribution in #3

Full Changelog: https://github.com/containerd/plugin/commits/v0.1.0