Added wsf_html documentation in the doc/workbook.

Also improved the structure of `wsf_html` library.
Added a few widgets.

doc/workbook/workbook.md

@@ -7,6 +7,7 @@
 * [Handling Requests: Header Fields](#header_fields)
 * [Generating Responses](#generating_responses)
 * [Handling Cookies](#handling_cookies) 
+* [Web User Interface](#wui) 
 * [EWF Deployment](#deployment)
 
 <a name="core"></a>
@@ -39,6 +40,11 @@ Before reading (or walking throught) the workbook, to get a quick overview of EW
 ## Generating Response
 [Generating Responses](./generating_response/generating_response.md)
 
+<a name="wui"></a>
+
+## Web User Interface
+[Web User Interface](./wui/readme.md) 
+
 <a name="handling_cookies"></a>
 
 ## Handling Cookies