+ Removed most explicit pathnames, use the standard make "VPATH" to let
make find the files for itself.
+ Added a "hardware variant" variable that allows compiging Sanguino and
Gen7 as well as "generic" arduino.
+ Allows overriding the MOTHERBOARD define from the Makefile
+ Removed the 'preprocessor' bit that wasn't needed, now just "include" the
files that are needed, since it allows gcc to show the right file/line
when displaying error/warnings.
+ Uses gcc's own dependency generator to generate the .d files, and
and include these instead of self-patching the makefile
Signed-off-by: Michel Pollet <buserror@gmail.com>