This PR moves all compile-time configuration to a single module,
simplifying documentation and access to these features.
Upcomfing features may be enabled either individually, or through a new
`chronosPreviewV4` catch-all designed to allow code to be prepared for
increased strictness in future chronos releases.
`-d:chronosDebug` may be used to enable the existing debugging helpers
together.
Jacek Sieka