Scan an assembly in order to create a DataContractContentSerializer

Resolves #100.
>When unit testing F# code, I rarely have a sut value, because the SUTs are functions, and functions are rarely values

I think that's a great and valuable observation! (May also fit into 140 chars.)

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According to the Arrange, Act, and Assert phases, the test could be written as:
```c#
[Theory, AutoData]
public void ScanCorrectlySerializesAttributedClassInstance(
    DataContractTestEventX @event)
{
    // Arrange
    var expected = XDocument.Parse(
        "<test-event-x xmlns:i=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns=\"http://grean.rocks/dc\">" +
        "  <number>" + @event.Number + "</number>" +
        "  <text>" + @event.Text + "</text>" +
        "</test-event-x>");
    var assembly = @event.GetType().Assembly;
    // Act
    var actual = DataContractContentSerializer.Scan(assembly);
    var result = XDocument.Parse(@event.AsSerializedString(actual));
    // Assert
    Assert.Equal(expected, result, new XNodeEqualityComparer());
}
```