Methods shouldn't be forced to `public`

[ShawnTheBeachy]

99% of the time that I'm mapping from an IDataReader to a model, I'm doing it with an accessor of internal. However, the generated extension method is public, which means my model is also forced to be public. This means that both the extension method and the model show up in auto-complete when I'm working in a project that references the project where I'm using the reader. It would be great if the GenerateDataReaderMapper allowed us to at least set the accessibility to internal, if it doesn't default to it.