v1.0.0-rc2

• [Breaking] Lifecycle hooks now take a context.
• Add fx.In and fx.Out which exposes optional and named types.
  Modules should embed these types instead of relying on dig.In and dig.Out.
• Add an Err method to retrieve the underlying errors during the dependency
  graph construction. The same error is also returned from Start.
• Graph resolution now happens as part of fx.New, rather than at the beginning
  of app.Start. This allows inspection of the graph errors through app.Err()
  before the decision to start the app.
• Add a Logger option, which allows users to send Fx's logs to different
  sink.
• Add fxtest.App, which redirects log output to the user's testing.TB and
  provides some lifecycle helpers.