[ADF-4152] Updated folder structure of core docs (#4415)

* [ADF-4152] Moved core library docs into subfolders

* [ADF-4152] Moved core library docs into subfolders

* [ADF-4152] Manual fixes to core doc file links

* [ADF-4152] Further automatic + manual link tidying

docs/core/services/storage.service.md

@@ -0,0 +1,50 @@
+---
+Title: Storage service
+Added: v2.0.0
+Status: Active
+Last reviewed: 2018-11-14
+---
+
+# [Storage service](../../../lib/core/services/storage.service.ts "Defined in storage.service.ts")
+
+Stores items in the form of key-value pairs.
+
+## Class members
+
+### Methods
+
+-   **clear**()<br/>
+    Removes all currently stored items.
+-   **getItem**(key: `string`): `string|null`<br/>
+    Gets an item.
+    -   _key:_ `string`  - Key to identify the item
+    -   **Returns** `string|null` - The item (if any) retrieved by the key
+-   **hasItem**(key: `string`): `boolean`<br/>
+    Is any item currently stored under `key`?
+    -   _key:_ `string`  - Key identifying item to check
+    -   **Returns** `boolean` - True if key retrieves an item, false otherwise
+-   **removeItem**(key: `string`)<br/>
+    Removes a single item.
+    -   _key:_ `string`  - Key to identify the item
+-   **setItem**(key: `string`, data: `string`)<br/>
+    Stores an item
+    -   _key:_ `string`  - Key to identify the item
+    -   _data:_ `string`  - Data to store
+
+## Details
+
+The service will check to see if
+[web storage](https://developer.mozilla.org/en-US/docs/Web/API/Storage/LocalStorage)
+is available on the browser. If it is available then the service will use it to
+store the key-value items persistently. Web storage can be used in a similar way to
+[cookies](cookie.service.md) but with a much higher size limit (several MB for
+web storage compared to a few KB for cookies). However, cookies are
+more widely supported by browsers and can be set to expire after a certain date.
+
+If local storage is not available then non-persistent memory storage within the app is
+used instead.
+
+## See also
+
+-   [Cookie service](cookie.service.md)
+-   [Content service](content.service.md)