chore(doc-gen): put typescript stuff into its own package

This means that we can now run just the d.ts file generation by running:

```bash
gulp docs/typings
```

In addition the type definition generation was messing with the other docs tasks
so separating it also fixes problems there.

docs/docs-package/templates/angular2/angular2.d.ts.template.html

@@ -0,0 +1,32 @@
+{% extends '../type-definition.template.html' %}
+{% block staticDeclarations %}
+// Angular depends transitively on these libraries.
+// If you don't have them installed you can run
+// $ tsd query es6-promise rx rx-lite --action install --save
+///<reference path="../es6-promise/es6-promise.d.ts"/>
+///<reference path="../rx/rx.d.ts"/>
+
+interface List<T> extends Array<T> {}
+interface Map<K,V> {}
+interface StringMap<K,V> extends Map<K,V> {}
+
+declare module ng {
+  type SetterFn = typeof Function;
+  type int = number;
+  interface Type extends Function {
+    new (...args);
+  }
+
+  // See https://github.com/Microsoft/TypeScript/issues/1168
+  class BaseException /* extends Error */ {
+    message: string;
+    stack: string;
+    toString(): string;
+  }
+  interface InjectableReference {}
+}
+{% endblock %}
+
+declare module "angular2/angular2" {
+  export = ng;
+}