docs:page: report entries

```
> thor docs:page vue /guide/introduction.html --debug
Entries: (1 KB, +1 KB)
  Updated: 0
  Created: 1
    + 1. Introduction  (Getting Started)
  Deleted: 0
Types:
  Updated: 0
  Created: 1
    + Guide
  Deleted: 0
Files: (0.1 MB, +0.1 MB)
  Updated: 0
  Created: 1
    + guide/introduction
  Deleted: 0
Done
```

lib/docs/core/doc.rb

@@ -87,8 +87,15 @@ module Docs
       end
 
       def store_page(store, id)
+        index = EntryIndex.new
+        pages = PageDb.new
+
         store.open(path) do
           if page = new.build_page(id) and store_page?(page)
+            index.add page[:entries]
+            pages.add page[:path], page[:output]
+            store_index(store, INDEX_FILENAME, index, false)
+            store_index(store, DB_FILENAME, pages, false)
             store.write page[:store_path], page[:output]
             true
           else
@@ -137,11 +144,11 @@ module Docs
         page[:entries].present?
       end
 
-      def store_index(store, filename, index)
-        old_json = store.read(filename) || '{}'
+      def store_index(store, filename, index, read_write=true)
+        old_json = read_write && store.read(filename) || '{}'
         new_json = index.to_json
         instrument "#{filename.remove('.json')}.doc", before: old_json, after: new_json
-        store.write(filename, new_json)
+        read_write && store.write(filename, new_json)
       end
 
       def store_meta(store)