Pull request to add in the gravity change equations to VirtualCalifornia/quakelib/src

I don't know why it's showing the .gitignore file, changes to that don't matter and I tried to untrack it.

Relevant changes are in VirtualCalifornia/quakelib/src to files:
QuakeLibOkada.h
QuakeLibOkada.cpp

Gravity change equations have been verified to match results in the Okubo paper, they're ready to go.