ViveDoom version 0.1.0

Release Notes:

• Minimal version of OpenVR virtual reality mode
• Includes positional tracking

Submit bug reports and feature requests at https://github.com/cmbruns/gz3doom/issues?q=is%3Aissue+is%3Aopen+label%3AOpenVR

Participate in the forum thread at https://forum.zdoom.org/viewtopic.php?f=59&t=56623