Applies configuration style changes used in production systems, pioneered by @enricosada:

• use member val instead of member __. - triggering eager evaluation to minimize deferred throwing of exceptions for invalid invocations
• use type Configuration to:
  • ensure referential transparency in implementation of type Arguments - no more EnvVar.tryGet global lookups
  • centralize and DRY keys for environment variables
  • allow easy transition to Microsoft.Extensions.Configuration (can use IConfigurationRoot.Item >> Option.ofObj instead of EnvVar.tryGet to avail of layered loading of Secrets from aggregated configurations)
• Roll out some naming and style changes from Equinox
  • Equinox.Stream -> Decider