Add a Doxyfile and preliminary module-level docs.

src/trace.h

@@ -1,5 +1,13 @@
 #pragma once
 
+/**
+** \defgroup trace Performance Tracing
+** Generates trace output that is compatible with speedscope.app,
+** chrome://tracing or ui.perfetto.dev for scrutining what each thread is doing
+** for optimization purposes.
+** @{
+*/
+
 #include <inttypes.h>
 #include <stddef.h>
 
@@ -22,3 +30,5 @@ void tf_trace_set_write_callback(tf_trace_t* trace, tf_trace_write_callback_t* c
 void tf_trace_raw(tf_trace_t* trace, const char* buffer, size_t size);
 
 void tf_trace_sqlite(tf_trace_t* trace, sqlite3* sqlite);
+
+/** @} */