Home dir in Makefiles


Was there a specific reason that lines https://github.com/ladislas/Bare-Arduino-Project/blob/master/Makefile-Linux.mk#L8 and https://github.com/ladislas/Bare-Arduino-Project/blob/master/Makefile-OSX.mk#L8 are not:

```
PROJECT_DIR = ~/MyArduinoProject
```

Thanks!