avr: Add 'erase' and 'start' commands for dfu

Signed-off-by: Nikita 'webconn' Maslov <wkernelteam@gmail.com>
Merge pull request #55 from nekromant/dfu-avr

deploy: Add 'erase' and 'start' commands for dfu-programmer

Acked-by: Andrew Andrianov <andrew@ncrmnt.org>