router sharding

@pmorie - started a branch for the router sharding document.  The intent is to put this into the `routing.md` after it is defined.  
@smarterclayton Upstream uses the binding type to encapsulate an action by the scheduler to associate a pod with a host.  The binding type is 'applied' to the pod during the binding .REST `Create` call.  If we want to follow upstream closely, we should have a similar type for the result of the route allocation (is it really just route scheduling?).  Will make an update for that.