Data structure for route execution
A PathTree contains a map of the known route paths. The values of the
tree are RhoRoute's that can generate a reply to a Request.
Create a new PathTree with the RhoRoute appended
Result type of the RhoRoute.
RhoRoute to append to the new tree.
A new PathTree containing the provided route.
Attempt to generate a Response by executing the tree.
Merge this tree with another PathTree