Update LLVM 5.0 release notes for clang.cindex changes

[jbcoe]

Summary

This patch should be applied to clang 5.0 release notes, NOT to trunk.

[hans]

Looks good to me!

Let me know if you'd like me to commit it for you.

docs/ReleaseNotes.rst

 New Issues Found
 ================
 
 - ...
 
 Python Binding Changes
 ----------------------
 
+Python bindings now support both Python 2 and Python 3. 
+
 The following methods have been added:
 
+- ``is_scoped_enum`` has been added to ``Cursor``.
+
+- ``exception_specification_kind`` has been added to ``Cursor``.
+
+- ``get_address_space`` has been added to ``Type``.
+
+- ``get_typedef_name`` has been added to ``Type``.
+
+- ``get_exception_specification_kind`` has been added to ``Type``.
+
 -  ...
 
 Significant Known Problems
 ==========================
 
 Additional Information
 ======================