Modernize the generator itself

Convert to ARC, use modern Objective-C syntax, and clean some stuff up.
Refactor the generated code a bit
Always include the namespace prefix when making nodes
Remove the nsPrefix method from complex types
Deduplicate enumeration values
Make a bunch of pointlessly public methods private
Remove unused <NSCopying> implementation
Extract some duplicated code
Sort project file
Strip all non-license comments from STS .m files

They're pretty much a textbook example of how to make code completely
unreadable with terrible and useless comments.
Remove some compatibility cruft for old versions of OS X
Eliminate some pointless macros
Allow looping over any fast enumerable
Deduplicate operation headers
Handle numeric non-enum simple types in attributes
Remove NSCoding stuff