Add .gitignore

Signed-off-by: Nikita 'webconn' Maslov <wkernelteam@gmail.com>
Rework AVR port

Fixed:

* Old SIGNALs -> ISR
* Change confusing redefinitions in port.h

Signed-off-by: Nikita 'webconn' Maslov <wkernelteam@gmail.com>