Add small howto into README.md about using yaal
Remove exmpales/Makefile as obsolete
Add Olimex's AVR-MT128 board
Disable macro poisoning from libavr

Macro poisoning is too powerfull as it also makes error in this case
```c
#pragma GCC poison FOOBAR

#ifdef FOOBAR
  // do something
#endif
```
Fix typecast to have any point
Enhancements for makefile to be interfaced from GUI
Make serial.hh work on boards with only one serial interface.
Fix indentation in autounion.hh
serial: Make it work again on atmega32u4.