update path to config.h in directory above

was getting a syntastic error that config.h is not found - indeed it
is not in the current directory, but in the directory above.  either
way, the correct path to the header should be used.
move function doc to header file add prototype

for atmel.c and atmel.h, move documentation about certain functions
from the c source file into the header file.  the header file is
generally what is available to someone using the atmel.c package
so the documentation should be there.  also added a few internal
function prototypes to atmel.c and added more explicit debug info.
update gitignore
add DFU command list to atmel.c comments