extmod/modwebrepl: Module to handle WebREPL protocol.

While just a websocket is enough for handling terminal part of WebREPL,
handling file transfer operations requires demultiplexing and acting
upon, which is encapsulated in _webrepl class provided by this module,
which wraps a websocket object.
diff --git a/py/objmodule.c b/py/objmodule.c
index d2a4d89..e334935 100644
--- a/py/objmodule.c
+++ b/py/objmodule.c
@@ -196,6 +196,9 @@
 #if MICROPY_PY_WEBSOCKET
     { MP_ROM_QSTR(MP_QSTR_websocket), MP_ROM_PTR(&mp_module_websocket) },
 #endif
+#if MICROPY_PY_WEBREPL
+    { MP_ROM_QSTR(MP_QSTR__webrepl), MP_ROM_PTR(&mp_module_webrepl) },
+#endif
 #if MICROPY_PY_FRAMEBUF
     { MP_ROM_QSTR(MP_QSTR_framebuf), MP_ROM_PTR(&mp_module_framebuf) },
 #endif