Add routeUrlWith for Gitlab-friendly deployments

[srid]

We already have routeUrl that produces "pretty" URLs (ie, without .html suffix),

ema/src/Ema/Route.hs

Lines 20 to 23 in e745650

	-- TODO: Allow a way to configure disabling stripping of .html, since not all
	-- static site hosts support pretty URLs.
	routeUrl :: forall r model. Ema model r => model -> r -> Text
	routeUrl model =

Some places like Gitlab do not support these kinds of URLs. Therefore, add a routeUrlWith that takes an extra argument telling it to whether to "prettify" the URL or not.

And then define a type like this,

data UrlStrategy
  = UrlPretty
  | UrlDirect

Ema users can then use either routeUrl or routeUrlWith UrlDirect to define their URL linking behaviour.