net-im/snac: new port

Snac is a simple, minimalistic ActivityPub instance.

It features:

• Lightweight, minimal dependencies
• Extensive support of ActivityPub operations.
• Multiuser
• Mastodon API support, so Mastodon-compatible apps can be used
• Simple but effective web interface
• Easily-accessed MUTE button
• Tested interoperability with related software
• No database needed
• Totally JavaScript-free

PR: 278385
Reviewed by: bofh