Adds support for RSocket composite metadata.

Renames Registry to RoutingTable implemented as an inverted
index as TagsMetadata. Inverted index uses RoaringBitmaps to save
memory and to make lookup very fast.

Implements RoutingTableRoutes as a view over RoutingTable.

Route is now an interface. The Route objects returned by
RoutingTableRoutes are backed by a predicate that uses the RoutingTable
rather than custom matching.

GatewayRSockectFactory moved to a top level class.

PendingRequestRSocket also has a top level Factory.

Load balancing is now handled by a Factory. Allows requests to ask
for specific types of load balancers in the future.

Implements proposed RouteSetup and Forwarding metadata types in
the Gateway. These should eventually be replaced by primitives in
rsocket-java. Also adds support to be encoded/decoded using
Frameworks Encoder/Decoder classes.

fixes gh-1236

src/checkstyle/checkstyle-suppressions.xml

@@ -27,4 +27,5 @@
 	<suppress files=".*XForwardedRemoteAddressResolver\.java" checks="FinalClass"/>
 	<suppress files=".*Route\.java" checks="FinalClass"/>
 	<suppress files=".*HystrixGatewayFilterFactory\.java" checks="AvoidNestedBlocks"/>
+	<suppress files=".*WellKnownKey\.java" checks="JavadocVariable"/>
 </suppressions>