message: Add isEmpty()
diff: @@ -56,6 +56,10 @@ class Selection {
  return this.end.line - this.start.line;
  }
  + isEmpty(): boolean {
  + return this.start.isEqualTo(this.end);
  + }
  +
  extendToStartOfLine(): Selection {
  return Selection.fromPositions(this.start.putAtStartOfLine(), this.end);
  }
  