Now compiles for Mac OS

 - Added Mac OS (i386, x86_64) target to project.
 - Used preprocessor to conditionally compile based on target (either
iOS device/sim or Mac OS)
 - Used basic appropriate alternatives for unavailable data (i.e. model
number of machine for device type, always off for cellular data
connectivity, etc)
Added header files as members to the new target
Fix a compiler warning

http://stackoverflow.com/questions/7765484/xcode-4-2-declaration-of-will
-not-be-visible-outside-of-this-function-wa
Fixed compiler warnings under Mac OS
Fixed possible bug with updating location and heading.

I have not managed to test this on a device yet, but I think there was
a bug here.

SCOcurrence instances start updating *heading* and *location* when
init'd. The delegate callback methods for updates to these values
stopped the updating, but for the other value.

`locationManager:didUpdateToLocation:fromLocation` was stopping the
heading updates, while `locationManager:didUpdateHeading` was stopping
location updates. I believe this would mean only one of the two would
ever be available, and it would be the first that got returned. It may
have also left the location manager updating the other value
indefinitely.