Const fixes, init fixes, some return values, C++11 for Xcode 5

4a1d066
I added missing const's to the process functions (matches underlying libpd which uses const as expected for the input buffers). 
I replaced the singleton initialization with a thread safe version (because it matters in my threaded app :)
I fixed the inited flags because I needed my threads to ignore the pd object until it is ready to run (and the init flag was not being initialized).
I added return values to the starts and sends (matching underlying libpd) because I need to know if they succeeded or not.

f3e4fe9
I upgraded the pbxproj file to Xcode 5 lib c++. Maybe that change is premature for most people, but I'm on all the new stuff, and maybe the diff is of interest to people looking to upgrade to iOS 7 dev.