Added missing .pch file, Implemented elevation functionality, Misc code refactoring

1. The XCode project was missing a .pch file that it needed to build. I removed *.pch from the .gitignore and added the necessary file.
2. I renamed lots of functions and variables (e.g. getDistance() to computeDistanceFrom()) so that they were more consistent with the Philadelphia Game Lab C++ Code Compliance.
3. Lots of superfluous code was condensed to be more concise, and vestigial code was removed.
4. Modifications were made to avoid passing around unitialized variables.
5. Elevation functionality was added so that the height of an audioObject in relation to the player is now taken into account when computing HRTFs.