Redo state management for Janet listeners.

Make more use of the built in GC code for abstracts to
be sure things are more correct. Issue before was streams could
be freed before IOCP events arrived.

src/include/janet.h

@@ -591,7 +591,6 @@ typedef enum {
     JANET_ASYNC_EVENT_HUP,
     JANET_ASYNC_EVENT_READ,
     JANET_ASYNC_EVENT_WRITE,
-    JANET_ASYNC_EVENT_CANCEL,
     JANET_ASYNC_EVENT_COMPLETE, /* Used on windows for IOCP */
     JANET_ASYNC_EVENT_USER
 } JanetAsyncEvent;
@@ -613,13 +612,9 @@ typedef JanetAsyncStatus(*JanetListener)(JanetListenerState *state, JanetAsyncEv
 struct JanetStream {
     JanetHandle handle;
     uint32_t flags;
-    /* Linked list of all in-flight IO routines for this stream */
-    JanetListenerState *state;
+    JanetListenerState *read_state;
+    JanetListenerState *write_state;
     const void *methods; /* Methods for this stream */
-    /* internal - used to disallow multiple concurrent reads / writes on the same stream.
-     * this constraint may be lifted later but allowing such would require more internal book keeping
-     * for some implementations. You can read and write at the same time on the same stream, though. */
-    int _mask;
 };
 
 /* Interface for state machine based event loop */
@@ -633,11 +628,6 @@ struct JanetListenerState {
     void *tag; /* Used to associate listeners with an overlapped structure */
     int bytes; /* Used to track how many bytes were transfered. */
 #endif
-    /* internal */
-    size_t _index;
-    int _mask;
-    uint32_t _sched_id;
-    JanetListenerState *_next;
 };
 #endif
 
@@ -928,6 +918,7 @@ struct JanetFiber {
      * in a multi-tasking system. It would be possible to move these fields to a new
      * type, say "JanetTask", that as separate from fibers to save a bit of space. */
     uint32_t sched_id; /* Increment everytime fiber is scheduled by event loop */
+    JanetListenerState *waiting;
     void *supervisor_channel; /* Channel to push self to when complete */
 #endif
 };