Added board.mk makefile with board specific defines
Linker files for F20x boards with 768k flash
libmaple/usb/stm32f1/usb.c: cosmetics.

Whitespace and comments.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
Merge branch 'HEAD' of git://github.com/leaflabs/libmaple.git