Added Formula for ios-class-guard

iOS class-guard is simple Objective-C obfuscator for Mach-O executables. More info about tool can be found here: https://github.com/Polidea/ios-class-guard.

Can a test be added to do something more substantial than e.g. `--version` or `--help`? See `cmake.rb` for an example of an application formula with a good test and `tinyxml2.rb` for an example of a library formula with a good test. Thanks!