Do you know about the ; style for rules that have only one line of commands? It helps reduce the number of tabs.

    %.html: %.pug ; pug -P $^

I find it super useful for compact Makefiles:

    %.html: %.pug    ; pug -P $^
    %.css:  %.styl   ; stylus $^
    %.js:   %.coffee ; coffee -c $^
    %.html: %.md     ; markdown $^ > $@
    clean: ; rm -rfv $(OBJECTS)

Also, worth making clean .PHONY since it's not a file.