Adding serial.set(Rx|Tx)BufferSize (#1931)

* Fix for https://github.com/Microsoft/pxt-microbit/issues/1929

* bump pxt

* updated docs

* fix default values

* moving dialogs to react

* moving to react

* typo

* typo

libs/core/serial.cpp

@@ -191,4 +191,23 @@ namespace serial {
       uBit.serial.redirect(USBTX, USBRX);
       uBit.serial.baud(115200);
     }
+
+    /**
+    * Sets the size of the RX buffer in bytes
+    * @param size length of the rx buffer in bytes, eg: 32
+    */
+    //% help=serial/set-rx-buffer-size
+    void setRxBufferSize(uint8_t size) {
+      uBit.serial.setRxBufferSize(size);
+    }
+
+    /**
+    * Sets the size of the TX buffer in bytes
+    * @param size length of the tx buffer in bytes, eg: 32
+    */
+    //% help=serial/set-tx-buffer-size
+    void setTxBufferSize(uint8_t size) {
+      uBit.serial.setTxBufferSize(size);
+    }
+
 }