Mention more potentially incompatible changes

Author: nwellnhof

NEWS

@@ -59,6 +59,11 @@ parser. Custom SAX parsers must use the "len" argument.
 
 xmlIOParseDTD doesn't allow null bytes at the end of the input anymore.
 
+Type and layout of conversion callbacks in struct xmlCharEncodingHandler
+were changed. Applications using libxml2's encoding conversion API
+should use functions xmlCharEncInFunc and xmlCharEncOutFunc instead of
+accessing the callbacks directly.
+
 ### New features
 
 Input callbacks can now be set on a parser context and an improved API
@@ -99,6 +104,9 @@ The xpointer() scheme now behaves like the xpath1() scheme.
 
 Several legacy symbols and the functions in xmlunicode.h were removed.
 
+Some unprefixed, internal macros like ATTRIBUTE_UNUSED were removed
+from public headers.
+
 ELF version information was removed.
 
 The shell was moved from libxml2 to xmllint. Several related functions