Tutorial: write page on routing

Create instructions and code samples on mapping URL parameters to different initial values in the application, and vice versa.

https://github.com/apache/royale-docs/blob/master/create-an-application/application-tutorial/routing.md

Open create-an-application/application-tutorial/routing.md in the linked royale-docs repository and review its existing tutorial structure. Add instructions and code samples showing how URL parameters map to different initial application values, and how those values map back to URL parameters; done means the routing tutorial covers both directions clearly.

Written by the indexing model from the issue text.