Makefile: Added generic make file

Added Makefile to compile the brightness utility. It has the all target, as well as the basic install, uninstall and clean targets.
Makefile: Added appropriate .PHONY directives.

Forgot to adde .PHONY directives for clean, install and uninstall.
Makefile: Added -Wall compiler flag.
brightness: Added and implemented brightness.c with main code.

The brightness utility can increase, decrease and show the brightness level.
Makefile: Edited install code to make root the owner and executor of the file.