Makefile: add 'dist' target

Makefile

@@ -46,3 +46,12 @@ install: all
 
 uninstall:
 	rm -f $(DESTDIR)$(PREFIX)/bin/i3lock
+
+dist: clean
+	[ ! -d i3lock-${VERSION} ] || rm -rf i3lock-${VERSION}
+	[ ! -e i3lock-${VERSION}.tar.bz2 ] || rm i3lock-${VERSION}.tar.bz2
+	mkdir i3lock-${VERSION}
+	cp *.c *.h i3lock.1 i3lock.pam Makefile LICENSE README i3lock-${VERSION}
+	sed -e 's/^GIT_VERSION:=\(.*\)/GIT_VERSION:=$(shell /bin/echo '${GIT_VERSION}' | sed 's/\\/\\\\/g')/g;s/^VERSION:=\(.*\)/VERSION:=${VERSION}/g' Makefile > i3lock-${VERSION}/Makefile
+	tar cfj i3lock-${VERSION}.tar.bz2 i3lock-${VERSION}
+	rm -rf i3lock-${VERSION}