Merge pull request #5 from ayanonagon/master

Make style more like standard Objective-C.
Fixed spelling mistake in README.

Said 'their' instead of 'the'.
Added basic formatting; checking to see if the string is gte 9, and non-null.
Added further validation, an NSString category, a method to find the type of card from a string, and tests for the new validation, need to add for the get type methods.
Fixed issue where the predicate was invalid and the wrong var was being passed into -predicateForType. Tests are also complete.
Updated README

Now includes new instructions as to how you can use the class methods and NSString category
Updated README

Thanked @ayanonagon.
Added further tests and validation to prevent the formatted string from being used if it’s invalid.
Merge branch 'master' of https://github.com/MaxKramer/ObjectiveLuhn
Removed NSLog and updated tests which were failing because of the NSParameterAsserts()
Make example project consume pod via Podfile.