This commit adds the following changes to router package:
* it refactors Advertise() function which now does only what
it claims to do: advertising
* various router packages functions/methods have been renamed to make
their functionality more obvious and more in line with what they actually do
* function documentation changes related to the above bullet points
We now manage routing table actions using dedicated functions run on
either registry or services in the registry.
Routing table now uses Route.Hash() instead of maintaining its own hash
struct filed which previously performed these operations.
Various names of variables have been changed to make them more concise.
* Changed router interface to return Advertisement channel
* Added default gateway route to the routing table if supplied
* Watch table for updates and advertise to the network
* We hash the routes on 3-tuple (Destination, Gateway, Network)
