doing god's work

Looks great. Enjoyed the example data elements. A few notes:

• Do you need to be logged in with an account on the instance that contains a group in order to be able to post in that group?
• Consideration for transferring group ownership to another group member
• I get the impression this is fully federate-able without requiring other instances to change any code
• If a group has a non-moderated join policy, perhaps a max_group_members setting could rate limit a group
• Maybe there could be a group setting that can prohibit remote joins (e.g. require group members to have an account on the instance to be able to join the group)

Addendum: for discoverability purposes, groups may be mentioned with the @ syntax, like:

Hey, join my new group! @soapbox-dev@gleasonator.com

In this case, messages must address the group in its cc field. Addressing the group in the to field means a message to the group. Addressing it in the cc field is just a mention.