Added a tool to log messages by connecting a simple flash chip directly to the SPI of the autopilot

Added a new module for the logging using a memory directly plugged on SPI.

The documentation is available here : http://wiki.paparazziuav.org/wiki/Micro_logger
Instead of hardcoding the UART, make it configurable from the module xml file (e.g. as `HS_LOG_UART`) and use the functions instead of the macros ```uart_check_free_space(&HS_LOG_UART, _x)```