feature request: Connection ID groups

[majestrate]

oxend rpc code, pysogs and many other code bases would greatly benefit from adding / removing connection ids into a group and being able to send to the group and everyone in the group gets that message sent to them.

Something akin to:

struct BuddyGroup
{
    std::unordered_set<ConnectionID> _buddies;
    
    void add(ConnectionID);
    void remove(ConnectionID);
    
    template<typename Args>
    void send(Args && ...) const; // blah blah blah send to all the buddies
};

[jagerman]

I think it would be simpler for the API to just be able to pass an unordered_set of ConnectionIDs as the first argument to omq.send(...) -- no need to store an (invalidatable) reference to the OxenMQ, and no need to wrap the unordered_set capabilities.

[majestrate]

true.