Decouple frees config

[pepegar]

In this PR I:

• create a bare minimum ConfigM tagless to be used wherever freestyle.tagless.config were used before
• remove a couple of @module annotations
• bump frees-todolist-libto v0.8.1
• bump sbt-freestyle to 0.3.23

FIXES #294

[L-Lavigne]

Great work! Could you update the docs accordingly? The code samples are executed via tut and are currently failing the build (https://travis-ci.org/frees-io/freestyle-rpc/jobs/388386394). Thanks!

[juanpedromoreno]

I'd suggest the following approach, more natural perhaps?

class ChannelConfig[F[_]](implicit S: Sync[F], C: ConfigM[F]) {

  val defaultHost: String = "localhost"
  val defaultPort: Int    = freestyle.rpc.server.defaultPort

  def loadChannelAddress(hostPath: String, portPath: String): F[ChannelForAddress] =
    for {
      config <- C.load
      host <- S.pure(
        Either
          .catchOnly[Missing](config.getString(hostPath)))
      port <- S.pure(Either.catchOnly[Missing](config.getInt(portPath)))
    } yield ChannelForAddress(host.getOrElse(defaultHost), port.getOrElse(defaultPort))

  def loadChannelTarget(targetPath: String): F[ChannelForTarget] =
    for {
      config <- C.load
      target <- S.pure(Either.catchOnly[Missing](config.getString(targetPath)))
    } yield ChannelForTarget(target.getOrElse("target"))

}

object ChannelConfig {
  def apply[F[_]](implicit S: Sync[F], C: ConfigM[F]): ChannelConfig[F] = new ChannelConfig[F]

  implicit def defaultChannelConfig[F[_]](implicit S: Sync[F], C: ConfigM[F]): ChannelConfig[F] =
    apply[F]
}

[juanpedromoreno]

Same here

[JesusMtnez]

LGTM

[fedefernandez]

Looks great, I've left an optional suggestion. Thanks

[fedefernandez]

I'm wondering if we could add a new method to this algebra:

def get[A](from: (Config) => A): F[Either[Missing, A]]

With the implementation:

def get[A](getValue: => A): F[Either[Missing, A]] =
  S.pure(Either.catchOnly[Missing](getValue))

[pepegar]

I think that, at some point in the near future, we'll reintroduce frees-config, and we could maybe add it there? this implementation is temporary. What do you think?

[fedefernandez]

Sounds good