extend PyUnicode C-API declarations

--HG--
extra : transplant_source : r5f%D6%7E%D3%9C%0A%A0%1C%9FX%E0%F6ji%13T%00%A4

CHANGES.rst

@@ -8,6 +8,8 @@ Latest
 Features added
 --------------
 
+* Missing C-API declarations in ``cpython.unicode`` were added.
+
 * Passing ``language='c++'`` into cythonize() globally enables C++ mode for
   all modules that were not passed as Extension objects (i.e. only source
   files and file patterns).