clarified signature;

clarified build process roles: "worker" vs. "build";

clarified database content; tuned signature;

tuned: prefer iterator.nextOption;

tuned whitespace and braces;

clarified signature: more uniform operations;

tuned signature: reduce boilerplate;

tuned signature;

proper clean_build of old data at start of new process --- allow to inspect remains of the last process;

more database content: formal end_build;

more operations;

clarified database content and prepare/init stages;