add support for escaped route segments

[mcansh]

in Remix you can escape route segments by surrounding it with [], so things like [slug.json] => slug.json end up being the segment, however you can't do that today in React Router.

With that being said you can't have a literal * as a route as it would behave like a splat/catch-all route. You can workaround that by checking params['*'] === '*', but that's less than ideal.