Improved flexibility

I've made some little improvements. 
* Added multirouting, which means sitemap can be generated from multiple routes.
* Added static parameters, static parameters will be parsed as a string to the route and won't be fetched from the entity
* Made entity parameter optional in case you want to have a route which points to static files, e.g. /{page_name} 

I've described these features and included some examples in the index.md.

Could you merge the changes?