backlight: update FreeBSD support

doc: improve documentation

backlight: now supports more commands

doc: fix manual page

make: simplify makefile, advertise clang

make: don't fix CC variable

backlight: use _XOPEN_SOURCE=700

backlight: search for card in Linux

backlight: fix for FreeBSD and pet a warning

make: use POSIX only commands

(0) -10 +10 tip

mercurial