renamed "isabelle log" to "isabelle build_log";

clarified structure;

tuned output;

clarified signature: proper abstract type;

clarified signature: support all arguments of Sessions.store();

tuned;

basic setup for "isabelle build_worker";

tuned comments;

tuned structure;

clarified terminology of "session build database", while "build database" is the one underlying Build_Process;

clarified modules;

clarified signature: reduce boilerplate;

clarified messages;

tuned signature;

tuned structure;

clarified signature;

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;