Add "variables" for path parameters

[zth]

Allow using "variables" for path parameter enums, like:

// Now
"/some/path/:status(online|offline|idle)"

// With variables
"/some/path/:status{onlineStatus}"

// In the config, or wherever makes sense
{
  routeVariables: {
    onlineStatus: ["online", "offline", "idle"]
  }
}

Means easier reuse, easier to keep in sync since you can setup the JS like you want, etc.