Add infrastructure changes to build the API documentation.

doxygen and graphviz are required. It's disabled by default, use
the BUILD_API_DOCS make(1) argument to enable it.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20100123013719-pkk3a3823cx09v8l

doc/Makefile

@@ -0,0 +1,24 @@
+#
+# Makefile to build the libxbps API documentation.
+#
+DOXYF	?=	xbps_api_doxyfile
+FORMAT	?=	png
+FILES	=	xbps_transaction_dictionary.$(FORMAT)
+FILES	+=	xbps_regpkgdb_dictionary.$(FORMAT)
+FILES	+=	xbps_pkg_props_dictionary.$(FORMAT)
+FILES	+=	xbps_pkg_files_dictionary.$(FORMAT)
+FILES	+=	xbps_binary_pkg_content.$(FORMAT)
+
+.PHONY: all
+all: $(FILES) doxygendocs
+
+$(FILES): %.$(FORMAT): %.dot
+	dot -T$(FORMAT) $< -o images/$@
+
+doxygendocs: $(FILES)
+	doxygen $(DOXYF)
+
+.PHONY: clean
+clean:
+	-rm -f images/*.$(FORMAT)
+	-rm -rf ../api