more efficient Markup_Tree, based on branches sorted by quasi-order;
renamed markup_node.scala to markup_tree.scala and classes/objects accordingly;
Position.Range: produce actual Text.Range;
Symbol.Index.decode: convert 1-based Isabelle offsets here;
added static Command.range;
simplified Command.markup;
Document_Model.token_marker: flatten markup at most once;
tuned;
use_thys [
"Integration",
"Isar",
"Local_Theory",
"Logic",
"ML",
"Prelim",
"Proof",
"Syntax",
"Tactic"
];