Addressing review suggestions and fixing asynchronous function calls.

This commit addresses @bartvde's review comments, adds more documentation, and fixes asynchronous function calls. Previously, when creating multiple processes with the same identifier, the describe callback would only have been called for the first process. This was fixed to move DescribeProcess handling from WPSProcess to WPSClient.

examples/wps-client.html

@@ -22,7 +22,9 @@
     <div id="map" class="smallmap"></div>
 
     <div id="docs">
-        <p>This example shows how simple it is to use the WPS Client. See
+        <p>This example shows how simple it is to use the WPS Client. It
+            buffers an intersection of a geometry and a feature, which is
+            accomplished by chaining two processes. See
         <a href="wps-client.js">wps-client.js</a> to see how this is done.</p>
     </div>
   </body>