Add a Doxyfile and preliminary module-level docs.

src/task.h

@@ -1,5 +1,14 @@
 #pragma once
 
+/**
+** \defgroup task Task
+** Task is responsible for running JS in C.  It exposes just what is needed for
+** sandboxed or trusted code, helps with communiciation between parent and
+** child processes, including function calls and async operations across the
+** boundaries.
+** @{
+*/
+
 #include <stdbool.h>
 
 #include "quickjs.h"
@@ -80,3 +89,5 @@ bool tf_task_send_error_to_parent(tf_task_t* task, JSValue error);
 char* tf_task_get_disconnections(tf_task_t* task);
 char* tf_task_get_debug(tf_task_t* task);
 char* tf_task_get_hitches(tf_task_t* task);
+
+/** @} */