Allow Audiences to be modified after creation to filter them by either a predicate or another audience.

[Narimm]

The concept here is to minimize the need to for loop through targets to send a message to a subset of the server audience, where that subset is not provided by the existing methods in audienceProvider eg. all(), world(),server(),permission(String) etc

It would be ideal to take the provided audience and filter it either by a predicate, which as discussed might need to be platform-specific, or by another audience set.
audienceProvider.permission("some.permission", somePredicate)

or in the case of another audience set.

AudienceProvide.all().exclude(AudienceProvider.world("someworld").sendmessage()

Consideration would need to made, as to whether the implementation is better optimized than example like the for loop below.

This would avoid code like

//from a bukkit plugin 
for(Permissible perm : targets)
        {
            if(perm == except)
                continue;
            
            if(perm instanceof CommandSender && (permission == null || perm.hasPermission(permission)) && (checker == null || checker.isValid((CommandSender)perm)))
                audienceProvider.audience((CommandSender) perm).sendMessage(message);
        }

[kezz]

Closing this based on the merge of #365.