Roll Observatory packages and add a roll script

packages/petitparser/lib/src/lisp/cons.dart

-part of lisp;
+part of petitparser.lisp;
 
-/**
- * The basic data structure of LISP.
- */
+/// The basic data structure of LISP.
 class Cons {
 
-  /** The head of the cons. */
+  /// The head of the cons.
   dynamic head;
 
-  /** The tail of the cons. */
+  /// The tail of the cons.
   dynamic tail;
 
-  /** Constructs a cons. */
+  /// Constructs a cons.
   Cons(this.head, this.tail);
 
   @override
   bool operator ==(other) {
     return other is Cons && head == other.head && tail == other.tail;
   }
 
   @override
   int get hashCode => 31 * head.hashCode + tail.hashCode;
 
@@ skipping 10 matching lines @@
       }
     }
     if (current != null) {
       buffer.write('. ');
       buffer.write(current);
     }
     buffer.write(')');
     return buffer.toString();
   }
 }