refactor: rename annotations to metadata

BREAKING CHANGE (maybe)

Well as long as our customers use public API this should not be a
breaking change, but we have changed import structure as well as
internal names, so it could be breaking.

import:
  angular2/annotations => angular2/metadata

Classes:
  *Annotations => *Metadata
  renderer.DirectiveMetadata => renderer.RendererDirectiveMetadata
  renderer.ElementBinder => renderer.RendererElementBinder
  impl.Directive => impl.DirectiveMetadata
  impl.Component => impl.ComponentMetadata
  impl.View => impl.ViewMetadata

Closes #3660

docs/public-docs-package/index.js

@@ -5,7 +5,7 @@ module.exports = new Package('angular-v2-public-docs', [basePackage])
 
 .config(function(readTypeScriptModules) {
   readTypeScriptModules.sourceFiles = [
-    'angular2/annotations.ts',
+    'angular2/metadata.ts',
     'angular2/change_detection.ts',
     'angular2/core.ts',
     'angular2/di.ts',