This changeset is made up of two parts: 1. Generalize the `Snap.Internal.Http.Server.httpServe` function by replacing the `Maybe FilePath` logging targets by a more generic `Maybe (ByteString -> IO ())` action, and decouple from `System.FastLogger` (except for two remaining helper functions) by moving the logger construction to the calling code in `Snap.Http.Server`. Ideally, `Snap.Internal.Http.Server` wouldn't know anything specific about the concrete `Sytem.FastLogger`, as that would be configured/glued together in `Snap.Http.Server`. 2. Add a `ConfigLog` data type for configuring the logging type in the `Config` record (to replace the previous `Maybe FilePath` type), and adapt all affected code.