Use hosted-git-info library for robust parsing of SSH URLs (git@host:path
and ssh://) in addition to HTTPS. SSH and HTTPS URLs for the same repo
are now properly deduplicated.
- Rewrote README intro to emphasize extensibility and pi packages
- Added Pi Packages section to README
- Created docs/packages.md covering install, sources, manifest, filtering
- Created docs/prompt-templates.md covering format and arguments
- Created docs/themes.md with overview linking to theme.md