Add new hook type "process": launch command with fork and catch result (rc/stdout/stderr) via callback

src/plugins/plugin.c

@@ -439,6 +439,7 @@ plugin_load (const char *filename)
         new_plugin->hook_command_run = &hook_command_run;
         new_plugin->hook_timer = &hook_timer;
         new_plugin->hook_fd = &hook_fd;
+        new_plugin->hook_process = &hook_process;
         new_plugin->hook_connect = &hook_connect;
         new_plugin->hook_print = &hook_print;
         new_plugin->hook_signal = &hook_signal;