Fixed include dir for lib header install

Makefile

@@ -90,6 +90,7 @@ $(LIBNAME).hpp: $(HDRS)
 HEADERSRCDIR := build
 else
 HEADERSRCDIR := src
+INCLUDEDIR := $(INCLUDEDIR)/$(LIBNAME)
 endif
 
 test:
@@ -106,7 +107,7 @@ install:
 endif
 	$(INSTALL) -d $(LIBDIR)
 	$(INSTALL) -m 644 $(OUTDIR)$(REALNAME) $(LIBDIR)
-	$(INSTALL) -d $(INCLUDEDIR)/$(LIBNAME)
+	$(INSTALL) -d $(INCLUDEDIR)
 	$(INSTALL) -m 644 $(HEADERSRCDIR)/$(LIBNAME).hpp $(INCLUDEDIR)
 ifeq ($(UNAME_S),Darwin)
 	cd $(LIBDIR) && ln -sf $(REALNAME) $(SONAME)