MatchOn property for [Frozen] attribute

Currently, the `[Frozen]` attribute (in the *AutoFixture.Xunit* package) freezes the type of the method argument it's applied to. For example

```c#
[Theory, AutoData]
public void MyTestMethod([Frozen]Foo foo, Bar sut)
{
    // Test goes here...
}
```

the `Foo` type would be frozen, which means that no matter how many instances of `Foo` created within this test case, the same instance would always be used.

It would be more flexible if the `[Frozen]` attribute had a `MatchOn` property, where the user could specify which sort of match to use; e.g.

```c#
[Theory, AutoData]
public void MyTestMethod([Frozen(MatchOn = Matches.ArgumentName)]Foo foo, Bar sut)
{
    // Test goes here...
}
```

which would mean that instead of matching on the type `Foo`, the `[Frozen]` attribute would match on the `foo` name. In this case, it would match any other `ParameterInfo` called `foo`.

This would enable scenarios where you'd want to test a class with this type of constructor:

```c#
public class Bar
{
    public Bar(Foo foo, Foo otherFoo) { }
}
```

By writing the above test, `Matches.ArgumentName` would ensue that only requests for a `ParameterInfo` called `foo` would be frozen. In other words, this would mean that the `Bar` instance would get the same instance for its `foo` constructor argument as the test gets its `foo` method argument, but the `otherFoo` constructor argument would be different.

I think that perhaps, this could also be used to deprecate the current `As` property, because instead, one could write something like:

```c#
[Theory, AutoData]
public void MyOtherTestMethod(
    [Frozen(MatchOn = Matches.ImplementedInterfaces)]Baz baz,
    Qux sut)
{
    // Test goes here...
}
```

Now, if `Baz` implements `IBaz` the `[Frozen]` attribute would also apply to `IBaz`, and so if the SUT's constructor is `public Qux(IBaz whatever)`, the `baz` test method parameter would still be matched to the `whatever` constructor argument.

It seems to me that `Matches` should be a `[Flags]` enum; something like:

```c#
[Flags]
public enum Matches
{
    Type = 0,
    ImplementedInterfaces = 1,
    BaseClass = 2,
    ArgumentName = 4,
    PropertyName = 8,
    FieldName = 16,
    MemberName = ArgumentName | PropertyName | FieldName
}
```

etc. There may be more.

The only reason to have an enum is to enable configuration of an attribute. The enum should as soon as possible be translated into an appropriate `OrRequestSpecification`.

This issue is a border-line [jump-in](http://nikcodes.com/2013/05/10/new-contributor-jump-in/) issue. The reason why the description is so long is not because it would be very complicated to implement (I think), but because I wanted to provide as much detail as possible. Still, if you decide to pick up this one and you have questions, feel free to ask.
To preserve history, here is some previous [discussion](https://github.com/AutoFixture/AutoFixture/commit/926d4379c2ac1c5d1eb6af53cdf6c5e7591b392b#commitcomment-3584774) around the `Matching` enum.