Creating RequestHandler

Changing the approach being used in iroh to hopefully be more of a
pipeline with a single generic handler.
Begun working on the stylesheet processor

Fixed up the import ordering for RequestHandler
Adding stylesheet processor

Setting up the stylesheet processor which includes a way to load
routes for so the processor can be loaded.
Tidied up the server module a little bit.
Got the processor writing the data
Setting up the path to be passed to the processor

Part of that is expanding the content_path from the config which
means that we expand any environment variables and expand the ~
and transform it to an absolute path.