Expose meta in Route objects (#602)

* Expose meta in Route objects

Expose route.meta to allow reading RouteConfig.meta in transition hooks.

Reasons: 
In 1.0, we used to pass Custom Fields( like `auth` in route configs, as the [document](http://router.vuejs.org/en/route.html#custom-fields) suggested), but in 2.0 these custom fields aren't exposed in `route` object.
I've noticed that in `RouteConfig`, there is an optional field `meta`, which i guess serves the functionality of the previous Custom Fields, judging from the fact that 1). It's type is any 2).there are no references of it in the source code. 
So I guess `meta` should be exposed in route objects, otherwise there is no need to define it in the first place.

* Update declarations.js

* Update create-matcher.js

Author: fnlctrl

flow/declarations.js

@@ -65,6 +65,7 @@ declare type Route = {
   fullPath: string;
   matched: Array<RouteRecord>;
   redirectedFrom?: string;
+  meta?: any;
 }
 
 declare type Matcher = (location: RawLocation, current?: Route) => Route;

src/create-matcher.js

@@ -126,6 +126,7 @@ export function createRoute (
 ): Route {
   const route: Route = {
     name: location.name || (record && record.name),
+    meta: (record && record.meta) || {},
     path: location.path || '/',
     hash: location.hash || '',
     query: location.query || {},