Move `HasServer (NamedRoutes routes)` instance
The instance has been moved to `Servant.Server.Internal`, as the
instances for other combinators. It is necessary so that the instance
can be re-exported from `Servant.Server` without circular imports.
Otherwise, users have to import `Servant.Server.Generic` manually ;
forgetting to do so will produce confusing error messages about the
missing instance.
Move `HasClient (NamedRoutes routes)` instance
Moved so that the instance is made available when importing
`Servant.Client`, avoiding possibly confusing errors when
`Servant.Client.Generic` isn't imported.
- Introduce SourceT, which is simple variant of "correct `ListT`".
There are another variants possible (like in `streaming`),
but I'm not sure there's much real difference.
- Introduce `Codensity`. There's a flag if people don't want to depend
on `kan-extensions`.
- `StreamGenerator` and `ResultStream` are both `SourceT`.
`Stream` combinator in `servant-client` uses `Codensity` for CPS.
- Add servant-machines, servant-conduit, servant-pipes
- Add streaming cookbook: just code, no explanations.
- Add a script to run streaming 'benchmarks'
