Feature/arbitrary process flow marking

[ysugimoto]

This PR provided feature that the user add arbitrary flow log on simulator.

Usage

Put @process [name] annotation comment on your subroutine and the simulator add flow log the snapshop status (scope, req, beresp, etc...) , and enable to see on a simulator response.

Example:

sub vcl_recv {
   ...
   // @process some_status
   set req.http.Foo = "bar";
}