ForValues now works with IEnumerable<string>

Issues resolved 
---
* resolves #35 

How it works
---

You can now run:

    // sieve.AcceptableValues = 1, 2, 3 (as ints)
    var acceptableValues = new List<string>{"1", "2", "3"};
    var Sieve = new EqualitySieve<ABusinessObject>()
        .ForProperty(x => x.AnInt)
        .ForValues(acceptableValues);

PS I  did this from an iPad. Isn't technology awesome?