hack based on Arjan van de Ven suggestion to reduce ELF footprint and

* elfgcchack.h doc/elfgcchack.xsl libxml.h: hack based on Arjan van de
  Ven suggestion to reduce ELF footprint and generated code. Based on
  aliasing of libraries function to generate direct call instead of
  indirect ones
* doc/libxml2-api.xml doc/Makefile.am doc/apibuild.py: added automatic
  generation of elfgcchack.h based on the API description, extended
  the API description to show the conditionals configuration flags
  required for symbols.
* nanohttp.c parser.c xmlsave.c include/libxml/*.h: lot of cleanup
* doc/*: regenerated the docs.
Daniel

include/libxml/xmlreader.h

@@ -17,6 +17,8 @@
 #include <libxml/relaxng.h>
 #endif
 
+#ifdef LIBXML_READER_ENABLED
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -359,5 +361,8 @@ XMLPUBFUN void XMLCALL
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* LIBXML_READER_ENABLED */
+
 #endif /* __XML_XMLREADER_H__ */