support string transformations on generated routes

Great gem! It works really well for single word routes. I wanted to use it to create multi-word routes and have a preference towards hyphens in URLs. Prior to this change, multi-word routes worked as follows:

```ruby
page :press_kit
```

would generate:

```ruby
get '/press_kit' => 'pages#press_kit', :as => :press_kit
```

I've added an options hash that supports passing a block to transform the route:

```ruby
page 'press_kit', :transform => { |page| page.dasherize }
```

This modifies the route, but leave the rest as before:

```ruby
get '/press-kit' => 'pages#press_kit', :as => :press_kit
```