Update demo activity.

Demo now consists of two activities:
  - DeviceListActivity shows all usb devices (including unsupported ones)
    in a ListView.
  - SerialConsoleActivity dumps the data stream for a device selected in
    DeviceListActivity.

UsbSerialLibrary/src/com/hoho/android/usbserial/util/HexDump.java

@@ -107,6 +107,10 @@ public class HexDump {
         return toHexString(toByteArray(i));
     }
 
+    public static String toHexString(short i) {
+        return toHexString(toByteArray(i));
+    }
+
     public static byte[] toByteArray(byte b) {
         byte[] array = new byte[1];
         array[0] = b;
@@ -124,6 +128,15 @@ public class HexDump {
         return array;
     }
 
+    public static byte[] toByteArray(short i) {
+        byte[] array = new byte[2];
+
+        array[1] = (byte) (i & 0xFF);
+        array[0] = (byte) ((i >> 8) & 0xFF);
+
+        return array;
+    }
+
     private static int toByte(char c) {
         if (c >= '0' && c <= '9')
             return (c - '0');