Add rayon as an optional dependency to via-router

[zacharygolba]

While writing a framework is very web 2.0, I found a way to stay relevant. We can allow path separators to be configurable as a char, and then add Rayon as an optional dependency to via-router. This way, it can be used as the starting point for an open-source DNS for a distributed web. This may also be beneficial for web servers with hundreds of routes, though I would expect the performance to be worse for the common use case.