Add net/listen and net/accept-loop.

These are the elements that make up net/server, which has been moved
into pure Janet instead.

src/boot/boot.janet

@@ -2722,6 +2722,28 @@
                 :on-status (or onsignal (make-onsignal env 1))
                 :source "repl"}))
 
+###
+###
+### Extras
+###
+###
+
+(defmacro- guarddef
+  [sym form]
+  (if (dyn sym)
+    form))
+
+(guarddef net/listen
+  (defn net/server
+    "Start a server asynchornously with net/listen and net/accept-loop. Returns the new server stream."
+    [host port &opt handler type]
+    (def s (net/listen host port type))
+    (if handler
+      (ev/go (fn [] (net/accept-loop s handler))))
+    s))
+
+(undef guarddef)
+
 ###
 ###
 ### CLI Tool Main