Tweaks and fixes

Hi!

First of all thanks for sharing your code.
I found it very useful!
Although in original state it doesn't work for me :(
I found some drawbacks, namely:
1) your code supposes that all images appear in files with extension, but methods like imageNamed: work well without extensions. [critical issue]
2) lack of support for scanning plist (but I think it would be very convenient, for example Info.plist) [enhancement]
3) using some benchmarking I found that your core scanning exec command via "find ... -exec" is 3x slower than simple pipe construction, i.e. "cat file | grep -o imageName" [enhancement]
4) also I propose trying to filter image names like: "Section_0.png", "Section_1.png", etc. These image names can possibly be created in code by [NSString stringWithFormat:@"Section_%d", (int)] constructions and not by its original file names. So I made tricky implementation of this feature (NB: it can be turned off by SHOULD_FILTER_ENUM_VARIANTS define) [new feature].

To sum up I implemented above points and if you will find it useful and correct — please include it in your original repository.
Thanks!