change attributes to (name * tree list) list
add function get_arg_cdata
add function opt_arg_cdata
modify function opt_arg_cdata
handle escamp_ attribute when parsing and printinx xml; remove it when printing
update changes
make xml_of_atts and string_of_xml_atts visible
attributes are now maps instead of lists
sorting names: sort by second string first, as first one will often be empty
update ocamldoc documentation