Add a Doxyfile and preliminary module-level docs.

src/packetstream.h

@@ -1,5 +1,11 @@
 #pragma once
 
+/**
+** \defgroup packetstream Packet Stream
+** Primitive helper for sending packets of known size across a pipe.
+** @{
+*/
+
 #include <stddef.h>
 
 typedef struct uv_pipe_s uv_pipe_t;
@@ -16,3 +22,5 @@ void tf_packetstream_send(tf_packetstream_t* stream, int packet_type, const char
 void tf_packetstream_set_on_receive(tf_packetstream_t* stream, tf_packetstream_onreceive_t* callback, void* user_data);
 void tf_packetstream_close(tf_packetstream_t* stream);
 uv_pipe_t* tf_packetstream_get_pipe(tf_packetstream_t* stream);
+
+/** @} */