workaround for occasional deadlock seen in HOL-Proofs with threads=2;

adapted to 3869b2400e22;

tuned output;

more options: client without implicit server startup;

console interaction with line-editor;

more flexible message formats;

clarified interrupt handling;

clarified signature;

option for console interaction;

more uniform Bytes.read_line/read_block operations;

auto update;

more comments;

more general TTY loop;

added Reply.NOTE for asynchronous notifications;

more operations;

more thorough init: purge inactive entries;

more generous timeout;

Entry.connection: proview password here; more robust checks;

clarified initial protocol;

ignore empty lines;

tuned;

more robust read_line after shutdown;

more implicit wire protocol;

tuned signature;

clarified server start, notably for invocation within regular Isabelle/Scala process;

tuned signature;

tuned signature;

clarified toString operations;

clarified socket connection;

server commands may access Server; Server.stop: proper shutdown; clarified signature;

tuned -- avoid regex matching on potentially large string; clarified message: command name could be malformed;

more robust build: prevent problems seen with Poly/ML eb94e2820013 on Mac OS X;