support for user-defined Isabelle/Scala command-line tools; misc tuning and clarification;
tuned signature;
clarified signature;
more robust: always package;
prefer explicit link;
provide --baseImagesUrl for VSCode extensions marketplace;
dynamic configuration of prettify-symbols-mode, similar to VSCoq;
tuned headers;
clarified modules;
more thorough build;
added admin tool "isabelle build_vscode";