psychxr-0.2.4rc3

Third release candidate for PsychXR.

There seems to be a bug introduced in the new version of the Oculus SDK causing an access violation error on exit when shutdown() is called at some point. It may be okay to avoid calling shutdown() to prevent this error for now. The same error occurs if you use a logging callback regardless if shutdown() is called or not. This issue seems to be related to the Oculus runtime, but might also be a bug with Cython or Python itself. Haven't been able to determine why the error occurs, but it seems harmless to avoid.