Add a Doxyfile and preliminary module-level docs.

src/taskstub.js.h

@@ -1,5 +1,12 @@
 #pragma once
 
+/**
+** \defgroup taskstub Task Stub
+** Task Stub is a poorly-named representation of a remote Task that can be
+** exposed to JS.
+** @{
+*/
+
 #include "quickjs.h"
 #include "uv.h"
 
@@ -18,3 +25,5 @@ tf_task_t* tf_taskstub_get_owner(const tf_taskstub_t* stub);
 tf_taskstub_t* tf_taskstub_create_parent(tf_task_t* task, uv_file file);
 void tf_taskstub_on_error(tf_taskstub_t* stub, JSValue error);
 void tf_taskstub_on_print(tf_taskstub_t* stub, JSValue arguments);
+
+/** @} */