Make libnotify optional (default on)

Conflicts:
	Makefile
	README
	cbatticon.c
Some changes
fixing git conflicts (one day I'll have to learn how git works)
some Makefile reorganisation
added 'Make options' in README
switched from 'ifndef WITHOUT_NOTIFY' to 'ifdef WITH_NOTIFY'
don't declare notification variable when libnotify is disabled (avoid unused variable warning)
Thank you, guys!
Set version to 1.4.0