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.

py/objmodule.c

@@ -196,6 +196,9 @@ STATIC const mp_rom_map_elem_t mp_builtin_module_table[] = {
 #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