Create NSURL+Directories.m
Add shortcuts to create NSURL's for various app folders
Create NSString+Debugging.m
Convert OSStatus numbers to 4 char codes if available

Eg. 'fmt?' in CoreAudio.  If the 4 char code is not available then the string is the original error integer.
Merge pull request #56 from Club15CC/master

Add convenience class methods to NSURL to create NSURL for various app directories