Refactor JSON and RPC API

src/rpc.h

@@ -4,16 +4,18 @@
 
 // JSON-RPC request descriptor
 struct mg_rpc_req {
-  struct mg_str frame;  // Request, e.g. {"id":1,"method":"add","params":[1,2]}
+  void **head;          // List of all RPC handlers
   mg_pfn_t pfn;         // Response printing function
   void *pfn_data;       // Response printing function data
-  void *fn_data;        // Endpoint handler data
+  void *handler_data;   // Endpoint handler data
+  void *process_data;   // Arbitrary user data
+  struct mg_str frame;  // Request, e.g. {"id":1,"method":"add","params":[1,2]}
 };
 
 void mg_rpc_add(void **head, struct mg_str method_pattern,
                 void (*handler)(struct mg_rpc_req *), void *handler_data);
 void mg_rpc_free(void **head);
-void mg_rpc_process(void **head, struct mg_str json, mg_pfn_t pfn, void *pfnd);
+void mg_rpc_process(struct mg_rpc_req *);
 
 // Helper functions to print result or error frame
 void mg_rpc_ok(struct mg_rpc_req *, const char *fmt, ...);