Added ChibiOS/RT + LWIP turtlesim demo

This demo works on a custom STM32F407 board, hosted at:
https://github.com/openrobots-dev/R2P_GW_module

Using:
  ChibiOS/RT version 2.5.2
  LWIP version 1.4.1
  National DP83848 PHY in RMII mode
  USB serial port emulation from ChibiOS/RT

It does not support error messages yet, since the logger (external personal
project)is still in alpha release.
Useful ChibiOS/RT shell commands can be issued through USB serial emulation.

This demo is released under GPLv3 for compatibility with ChibiOS/RT.

Andrea Zoppi