Expose module Data.Text.Format.Types.Internal.

Hi.
In some cases, there is need to construct Format in some way. In my case, it's localization: text format strings for messages in various languages are loaded from file. Data.Text.Format.Types.Internal module is not imported by default when someone imports simply Data.Text.Format, so, I think, there is really no danger that someone will use this module unintentionally.