Added ChangeLog generator code

Makefile.am

@@ -3,4 +3,26 @@ SUBDIRS = swe/src src docs/reference/swe-glib
 
 DISTCHECK_CONFIGURE_FLAGS = --enable-gtk-doc
 
+MAINTAINERCLEANFILES = ChangeLog
+
+distclean-local:
+	if test "$(srcdir)" = "."; then :; else \
+	    rm -f ChangeLog; \
+	fi
+
+ChangeLog:
+	$(AM_V_GEN) if test -d "$(srcdir)/.git"; then \
+	    (GIT_DIR=$(top_srcdir)/.git ./missing --run git log -M -C --name-status --date=short --no-color) | fmt --split-only > $@.tmp \
+	    && mv -f $@.tmp $@ \
+	    || ($(RM) $@.tmp; \
+	        echo Failed to generate ChangeLog, your ChangeLog may be outdated >&2; \
+	        (test -f $@ || echo git log is required to generate this file >> $@)); \
+	else \
+	    test -f $@ || \
+	    (echo A git checkout and git log is required to generate ChangeLog >&2 && \
+	    echo A git checkout and git log is required to generate this file >> $@); \
+	fi
+
+.PHONY: ChangeLog
+
 -include $(top_srcdir)/git.mk