Add install and uninstall target to Makefile

This PR closes some gaps in the makefile. It follows GNU coding standards and conventions at https://www.gnu.org/prep/standards/standards.html. It is not specific to GNU, and most of the world follows it.

Makefile

@@ -1,3 +1,25 @@
+# For GNU conventions and targets see https://www.gnu.org/prep/standards/standards.html
+# Using GNU standards makes it easier for some users to keep doing what they are used to.
+
+# 'mkdir -p' is non-portable, but it is widely supported. A portable solution
+# is elusive due to race conditions on testing the directory and creating it.
+# Anemic toolchain users can sidestep the problem using MKDIR="mkdir".
+
+AR = ar
+ARFLAGS = cr
+RM = rm -f
+RANLIB = ranlib
+MKDIR = mkdir -p
+
+INSTALL = install
+INSTALL_PROGRAM = $(INSTALL)
+INSTALL_DATA = $(INSTALL) -m 044
+
+prefix = /usr/local
+bindir = $(prefix)/bin
+libdir = $(prefix)/lib
+includedir = $(prefix)/include
+
 all: xmltest staticlib
 
 rebuild: clean all
@@ -12,15 +34,41 @@ effc:
         -Wno-unused-parameter -Weffc++ xmltest.cpp tinyxml2.cpp -o xmltest
 
 clean:
-	$(RM) *.o xmltest libtinyxml2.a
+	-$(RM) *.o xmltest libtinyxml2.a
+
+# Standard GNU target
+distclean:
+	-$(RM) *.o xmltest libtinyxml2.a
 	
 test: clean xmltest
 	./xmltest
 
+# Standard GNU target
+check: clean xmltest
+	./xmltest
+
 staticlib: libtinyxml2.a
 
 libtinyxml2.a: tinyxml2.o
-	$(AR) $(ARFLAGS)s $@ $^
+	$(AR) $(ARFLAGS) $@ $^
+	$(RANLIB) $@
 	
 tinyxml2.o: tinyxml2.cpp tinyxml2.h
 
+directories:
+	$(MKDIR) $(DESTDIR)$(prefix)
+	$(MKDIR) $(DESTDIR)$(bindir)
+	$(MKDIR) $(DESTDIR)$(libdir)
+	$(MKDIR) $(DESTDIR)$(includedir)
+
+# Standard GNU target.
+install: xmltest staticlib directories
+	$(INSTALL_PROGRAM) xmltest $(DESTDIR)$(bindir)/xmltest
+	$(INSTALL_DATA) tinyxml2.h $(DESTDIR)$(includedir)/tinyxml2.h
+	$(INSTALL_DATA) libtinyxml2.a $(DESTDIR)$(libdir)/libtinyxml2.a
+
+# Standard GNU target
+uninstall:
+	$(RM) $(DESTDIR)$(bindir)/xmltest
+	$(RM) $(DESTDIR)$(includedir)/tinyxml2.h
+	$(RM) $(DESTDIR)$(libdir)/libtinyxml2.a