Register a Chronology by its ID and type for lookup by {@link #of(string)}.
Chronologies must not be registered until they are completely constructed.
Specifically, not _in the constructor of Chronology.
@param chrono the chronology to register; not null
@return the already registered Chronology if any, may be null
Register a Chronology by its ID and type for lookup by {@link #of(string)}. Chronologies must not be registered until they are completely constructed. Specifically, not _in the constructor of Chronology.
@param chrono the chronology to register; not null @return the already registered Chronology if any, may be null