Convert dashes in scope/slice URL fragments to underscores in URL helpers

[svoop]

By convention (better SEO etc), dashes are preferred over underscores in URLs, but this results in ugly helpers. Here's an example:

# config/routes.rb

module Dashy
  class Routes < Hanami::Routes

    get "foo", to: "action.foo", as: :foo

    scope "myscope" do
      get "foo", to: "action.foo", as: :foo
    end

    scope "my-scope" do
      get "foo", to: "action.foo", as: :foo
    end

    slice :myslice, at: "/myslice" do
      get "foo", to: "action.foo", as: :foo
    end

    slice :my_slice, at: "/my-slice" do
      get "foo", to: "action.foo", as: :foo
    end
  end
end

The following routes and URL helpers are created:

GET  /foo            action.foo   as :foo
GET  /myscope/foo    action.foo   as :myscope_foo
GET  /my-scope/foo   action.foo   as :"my-scope_foo"  <--
GET  /myslice/foo    action.foo   as :myslice_foo
GET  /my-slice/foo   action.foo   as :"my-slice_foo"  <--

For the URL helpers, the dashes should be converted to underscores like so:

GET  /foo            action.foo   as :foo
GET  /myscope/foo    action.foo   as :myscope_foo
GET  /my-scope/foo   action.foo   as :my_scope_foo   <--
GET  /myslice/foo    action.foo   as :myslice_foo
GET  /my-slice/foo   action.foo   as :my_slice_foo   <--

Discussion: https://discourse.hanamirb.org/t/route-scopes-with-dashes/1120