UseGiraffeErrorHandler chaining support

[draganjovanovic1]

UseGiraffeErrorHandler ApplicationBuilder extension modified (ignore removed) to support chaining since it should probably never be the last middleware in the pipeline.

app.UseCors(configureCors)
    .UseGiraffeErrorHandler(errorHandler)
    .UseAuthentication()
    .UseGiraffe webApp

vs

app.UseCors configureCors |> ignore
app.UseGiraffeErrorHandler errorHandler
app.UseAuthentication() |> ignore
app.UseGiraffe webApp

[dustinmoris]

Nice, yes that makes sense. I wasn't thinking about chaining when I wrote the middleware, but I think your PR makes a lot more sense and is more incline with ASP.NET Core 👍