Refactoring on the doxygen generation

doc/Makefile.am

@@ -0,0 +1,27 @@
+apache:
+	$(DOXYGEN) doxygen-apache
+	touch apache.stamp
+
+iis:
+	$(DOXYGEN) doxygen-iis
+	touch iis.stamp
+
+nginx:
+	$(DOXYGEN) doxygen-nginx
+	touch nginx.stamp
+
+standalone:
+	$(DOXYGEN) doxygen-standalone
+	touch standalone.stamp
+
+
+if BUILD_APACHE2_MODULE
+all-local: apache
+endif
+
+if BUILD_STANDALONE_MODULE
+all-local: iis nginx standalone
+endif
+
+clean-local:
+	rm -rf apache iis nginx standalone