Using type real does not require a separate logic now.

merged

tuned text about "value" and added note on comments.

simplified command status: interpret stacked markup on demand;

event_bus.scala rather belongs to system plumbing;

some derived operations on Text.Range;

specific types Text.Offset and Text.Range; minor tuning;

moved Text_Edit to Text.Edit; tuned;

moved History/Snapshot to document.scala;

renamed raw_results to raw_protocol;

rename "unit" to "atom", to avoid confusion with the unit type;

document commands: maintain transition as future (wrt. potentially slow Outer_Syntax.prepare_command), refrain from second Toplevel.put_id;

use Synchronized.var and prevent global CRITICAL sections in this hot spot;

renamed create_id to new_id;

more explicit / functional ML version of document model; tuned;

renamed class Document to Document.Version etc.; renamed Change.prev to Change.previous, and Change.document to Change.current; tuned;