Manifest system

• [ ] Allow plugins to exist in their own repos
• [ ] Specify options supported by the plugin
• [ ] Specify permissions supported by the plugin
• [x] Specify help text

Would plugins be able to be installed on the fly? e.g. !!plugin install foo/bar or would these need to be defined in composer in the repo only?

Adding new plugins hot would be for a few reasons but probably doable a long way down the line.