Cleaned up Makefile.

Moved away from using git clean in the clean Makefile target.

Added man page and updated Makefile targets.

Also added a bit of sanitation on provider; forcing basename.

Added information about provider env var in help.

Added short-hand flag variants and support for custom backlight provi…

…ders.

Changed how we're setting command line flags.

Also adding the ability to explicitly set the brightness to a value.

Able to increase and decrease the brightness by step with command lin…

…e flags.