uasyncio: Add StreamReader.close() method.

uasyncio/uasyncio/__init__.py

@@ -89,6 +89,10 @@ class StreamReader:
             log.debug("StreamReader.readline(): res: %s", res)
         return res
 
+    def close(self):
+        yield IOReadDone(self.s)
+        self.s.close()
+
     def __repr__(self):
         return "<StreamReader %r>" % self.s