After this change all peer_data functions consistently
use stream_id rather than some "sub" object whose
data type is complicated by all sort of fields that
don't really concern how we track subscribers.
The goal here is to make all our peer_data functions
basically work in id space. Passing a full `sub`
to these functions is a legacy of when subscriber
info was attached to a full stream "sub" object,
but we don't care about anything sub-related
(color, description, name, etc.) when we are
dealing with subscriptions.
When callers pass in stream_id, you can be more
confident in a quick skim of the code that we're
not mutating anything in the "sub".
This de-clutters stream_data a bit. Since our
peer data is our biggest performance concern,
I want to contain any optimizations to a fairly
well-focused module.
The name `peer_data` is a bit of a compromise,
since we already have `subs.js` and we use
`sub` as a variable name for stream records
throughout our code, but it's consistent with
our event nomenclature (peer/add, peer/remove)
and it's short while still being fairly easy
to find with grep.
Steve Howell