Add support for `dynamic` members

Currently, the following type definition, which has a `dynamic` member, causes the code generator to fail:

``` C#
[GenerateSerializer]
public class TelemetryMessageValue
{
[Id(0)]
public string Name { get; set; }
[Id(1)]
public DateTimeOffset Timestamp { get; set; }
[Id(2)]
public dynamic Value { get; set; }

public TelemetryMessageValue(string name, dynamic value, DateTimeOffset? timestamp = null)
{
this.Name = name;
this.Value = value;
this.Timestamp = timestamp ?? DateTimeOffset.Now;
}
}
```

We should treat `dynamic` similarly to `object`.