Specs: rename sky:core to dart:sky

sky/specs/script.md

 Sky Script Language
 ===================
 
 The Sky script language is Dart.
 
 The way that Sky integrates the module system with its script language
 is described in [modules.md](modules.md).
 
 When an method defined as ``external`` receives an argument, it must
 type-check it, and, if the argument's value is the wrong type, then it
@@ skipping 13 matching lines @@
 
 ```dart
 const nonnull = const Object();
 ```
 
 The ``@nonnull`` annotation does nothing in code not marked
 ``external``, but it has been included anyway for documentation
 purposes. It indicates places where providing a null is a contract
 violation and that results are therefore likely to be poor.
 
-The following definitions are exposed in ``sky:core``:
+The following definitions are exposed in ``dart:sky``:
 
 ```dart
 abstract class AutomaticMetadata {
   const AutomaticMetadata();
   void init(DeclarationMirror target, Module module);
 
   static void runLibrary(LibraryMirror library, Module module) {
     library.declarations.values.toList()..sort((DeclarationMirror a, DeclarationMirror b) {
       bool aHasLocation;
       try {
@@ skipping 53 matching lines @@
   to a superclass' constructor, wherein the subclass' constructor has
   the same arguments as the superclass' constructor and does nothing
   but invoke that superclass' constructor with the same arguments. The
   syntax for defining this is, within the class body for a class
   called ClassName:
 
 ```dart
      ClassName = SuperclassName;
      ClassName.namedConstructor = SuperclassName.otherNamedConstructor;
 ```