Isolate RoutingService functionality

[spockz]

An interesting part of Finatra is how it builds on top of Finagle to do routing of (external) services. This is available in com.twitter.finatra.http.internal.routing.RoutingService which is internal.

Expected behavior

Able to use the RoutingService from Scala without any dependencies on twitter server or others.

Actual behavior

Currently the RoutingService is not available in Scala because it is internal/package private to http. The java compiler doesn't care (becomes it becomes public in jvm bytecode anyway.). Additionally, it is part of the http package which drags in a whole slew of other dependencies.

The benefit of the RoutingService in Finatra over the one in Finagle is that the Finagle one doesn't support path parameters.

[cacoco]

@spockz thanks for the issue, we'll take a look into what we can do.