Add functions PyUnicode_Append() and PyUnicode_AppendAndDel() that mirror

PyString_Concat() and PyString_ConcatAndDel() (the name PyUnicode_Concat()
was already taken).

Change PyObject_Repr() to always return a unicode object.

Update all repr implementations to return unicode objects.

Add a function PyObject_ReprStr8() that calls PyObject_Repr() and converts
the result to an 8bit string.

Use PyObject_ReprStr8() where using PyObject_Repr() can't be done
straightforward.

Modules/zipimport.c

@@ -203,7 +203,7 @@ zipimporter_repr(ZipImporter *self)
 		PyOS_snprintf(buf, sizeof(buf),
 			      "<zipimporter object \"%.300s\">",
 			      archive);
-	return PyString_FromString(buf);
+	return PyUnicode_FromString(buf);
 }
 
 /* return fullname.split(".")[-1] */