PhotoLinker specifications

This update includes significant changes and I need your help finding bugs. The entire codebase has been refactored in order modernize the code and make PhotoLinker more reliable. Most notably, PhotoLinker's memory management has transitioned to automatic reference counting (ARC) from garbage collection (GC). This represents a huge amount of work and, if all goes smoothly, you should notice no changes other than fewer random crashes. However, because the so much of the underlying code has changed, there may be some new bugs introduced in this version. Please send me bug reports and crash reports.

Also note that the code is now 64-bit only. This means that there are some machines that are capable of running 10.6, but are not capable of running PhotoLinker.