Documentation and better error message for span support
Created by: keichi
Documentation says:
See Supported Engines for engines that support the span feature (e.g. BP3).
However, Supported Engines does not mention if an engine supports spans.
In addition, if you try to use spans with an engine without span support, it will throw a runtime error:
what(): ERROR: Engine derived class SstWriter doesn't implement function DoPut
This error message does not mention about spans and might be confusing for end users.