Allow callbacks (Do/Does) before Returns

[Jason31569]

Referencing issue #98...

While doing something like stuffDoer.Calculate().Returns(42).AndCalls(x => blah()); works, it is would make a lot more sense to be able to do something like stuffDoer.Calculate(something).Do(x => { }).Returns(42); instead

Take the below example

var items = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

var a = items.Where(x => x % 2 == 0).Skip(3).ToArray();
var b = items.Skip(3).Where(x => x % 2 == 0).ToArray();

Because execution is from left to right a=[8, 10], and b=[4, 6, 8, 10]

We are used to reading (and even expecting) statements to work from left to right. Someone new to NSubstitute (like myself) could find this confusing, and would not expect the trailing Do to run before the Returns