sidekick root data: set buffer length to avoid crash of initial caret move;
separate Markup_Node, Markup_Tree, Markup_Text;
added Markup_Text.flatten;
Command.type_at: null-free version;
eliminated Command.RootInfo;
simplified printing of TypeInfo, RefInfo;
added Command.content(Int, Int);
/* dummy class to make ant javadoc work */
package isabelle;
public class Dummy { }