[New Feature] routerNamespace ( nested Namespaces )

[Greenrenge]

This pull request is to enable creating namespace routes as nested to another namespace route.
GET /foo/bar/bar would return 'inner bar'

  const fooRoutes = withNamespace('/foo')
  const innerBar = routerNamespace(
     get('/', () => 'inner bar')
   )

  const innerFoo = routerNamespace(
    get('/', () => 'inner foo'),
    innerBar('/bar')
  )

  const routes = router(
    fooRoutes(
        get('/', () => 'foo'), 
         innerFoo('/bar')
     )
  )

[coveralls]

Coverage remained the same at 100.0% when pulling 72fcf33 on Greenrenge:master into b551f42 on pedronauck:master.