Added WSF_REQUEST.path_parameter (a_name): detachable WSF_VALUE
- fill path_parameters using `import_raw_path_parameters"
when executing the route
- reset to previous value with reset_path_parameters (..),
just in case the request is executed via severals routes.
The descendant has to implement the function
response (ctx: C; req: WSF_REQUEST): WSF_RESPONSE_MESSAGE
Added related features and class in WSF_ROUTER to be able to use agent easily.