Add a filter option to allow clients to send addresses
and match outputs against those bitcoin addresses so
only transactions that spend those outputs match will
be incuded in the result.
Add a session state so clients can send a filter
and just reuse that filter in subsequent calls.
Demote the old RPC one to Legacy.
The old is still useful as it allows the 'verbose' version, but it uses
lots of deprecated tech and thus doesn't scale.
The change signifies that the server is not just for admin purposes it
will become the preferred way for all subnet-local interactions.
Notice that we still have the JSON based RPC protocol as fallback.
TomZ