build(make): add target uninstall

GNUmakefile

@@ -23,10 +23,16 @@ install-bin: hicolor
 install-include: hicolor.h
 	install -m 0644 $< $(DESTDIR)$(PREFIX)/include
 
+uninstall: uninstall-bin uninstall-include
+uninstall-bin:
+	-rm $(DESTDIR)$(PREFIX)/bin/hicolor
+uninstall-include:
+	-rm $(DESTDIR)$(PREFIX)/include/hicolor.h
+
 release: clean-no-ext test
 	cp hicolor hicolor-v"$$(./hicolor version | head -n 1 | awk '{ print $$2 }')"-"$$(uname | tr 'A-Z' 'a-z')"-"$$(uname -m)"
 
 test: all
 	tests/hicolor.test
 
-.PHONY: all clean clean-exe clean-no-ext install install-bin install-include release test
+.PHONY: all clean clean-exe clean-no-ext install install-bin install-include release test uninstall uninstall-bin uninstall-include