v1.7.3

1. Addition of an is_union() method in the type_traits module.

2. type_traits.smart_pointer_traits will now classify std::shared_ptr as a
   smart pointer (only boost::shared_ptr was recognized before)

3. Fix a regression in undname_creator_t.format_argtypes

4. C++xx flags are now correctly passed to CastXML. Allowed flags are:
   "-std=c++98", "-std=c++03", "-std=c++11", "-std=c++14", "-std=c++1z"
   Thanks to Mark Moll for the fix.

5. Add better support for "typedef (class|struct) {} foo;" syntax when using
   CastXML. GCCXML did not recognize the typedef. Fetching these
   declarations can now be done with: .typedef("foo") or .class_("foo").

6. Add support for the future llvm 3.9. As in release v1.7.1, new structs and
   typedefs are now exposed by llvm, which broke pyplusplus.
   In this case these are __NSConstantString_tag and __NSConstantString.
   The two declarations are now hidden from the declarations tree, but can still
   be generated by using the config.flags = ["f1"] option.

7. Multiple fixes to adapt default arguments in functions for py++. Using the
   latest version of CastXML is recommended. This makes sure default arguments
   for function parameters are correctly defined, so that py++ can process them.

8. Fix for exception when using castxml + gcc5 + std=c++11 and maps.

9. Removed unittest2 dependency for testing with python 2.6

10. Testing: test with std::tr1 unordered containers for gcc >= 4.4.7 and castxml

11. Cosmetic fix for generator name printed to stdout when launching unit tests

12. Fix simple typo in example.py comment

Thanks to the following people for their contribution to this release:
Mark Moll, Ashish Sadanandan, Mark Oates