Merge pull request #600 from OSVR/winfixes
Some windows build fixes
Use Eigen's definition of pi for cross-platform compat
Be sure not to need compiled date_time for interprocess.
Merge pull request #598 from OSVR/fix-typo
Add missing include installs
Add missing headers to install
Bump VRPN submodule to silence warnings
Build everything as position-independent
Upgrade vendored Eigen to 3.3.7, and try searching first.