allow 'await' in the REPL and added os.sleepAsync()

doc/quickjs.texi

@@ -368,6 +368,9 @@ optional properties:
   @item backtrace_barrier
   Boolean (default = false). If true, error backtraces do not list the
   stack frames below the evalScript.
+  @item async
+  Boolean (default = false). If true, @code{await} is accepted in the
+  script and a promise is returned.
   @end table
 
 @item loadScript(filename)
@@ -769,6 +772,12 @@ write_fd]} or null in case of error.
 @item sleep(delay_ms)
 Sleep during @code{delay_ms} milliseconds.
 
+@item sleepAsync(delay_ms)
+Asynchronouse sleep during @code{delay_ms} milliseconds. Returns a promise. Example:
+@example
+await os.sleepAsync(500);
+@end example
+
 @item now()
 Return a timestamp in milliseconds with more precision than
 @code{Date.now()}. The time origin is unspecified and is normally not