docs(http/toh-6): improve references to in-mem-web-api (#2964)

Author: wardbell

public/docs/ts/latest/guide/server-communication.jade

@@ -32,8 +32,8 @@ block includes
       <li> [Search parameters](#search-parameters).</li>
       <li> [More fun with observables](#more-observables).</li>
     </ul>
-  - [Guarding against Cross-Site Request Forgery](#xsrf)
-  - [Appendix: Tour of Heroes in-memory server](#in-mem-web-api).
+  - [Guarding against Cross-Site Request Forgery](#xsrf).
+  - [Appendix: Tour of Heroes _in-memory web api_](#in-mem-web-api).
 
   A <live-example>live example</live-example> illustrates these topics.
 
@@ -669,14 +669,18 @@ a#in-mem-web-api
   The *get heroes* scenario would work,
   but since the app can't save changes to a JSON file, it needs a web API server.
   Because there isn't a real server for this demo, 
-  it uses an *in-memory web API simulator* instead.
+  it substitutes the Angular _in-memory web api_ simulator for the actual XHR backend service.
 
 .l-sub-section
   :marked
-    The in-memory web api is not part of the Angular core.
-    It's an optional service in its own `angular-in-memory-web-api` library
-    installed with npm (see `package.json`) and
-    registered for module loading by SystemJS (see `systemjs.config.js`).
+    The in-memory web api is not part of Angular _proper_. 
+    It's an optional service in its own 
+    <a href="https://github.com/angular/in-memory-web-api" target="_blank" title="In-memory Web API"><i>angular-in-memory-web-api</i></a>
+    library installed with npm (see `package.json`).
+
+    See the
+    <a href="https://github.com/angular/in-memory-web-api/blob/master/README.md" target="_blank" title='In-memory Web API "README.md"'><i>README file</i></a>
+    for configuration options, default behaviors, and limitations.
 
 :marked
   The in-memory web API gets its data from !{_a_ca_class_with} a `createDb()`

public/docs/ts/latest/tutorial/toh-pt6.jade

@@ -91,10 +91,9 @@ block http-providers
 
 block backend
   :marked
-    We're importing the  `InMemoryWebApiModule` and adding it to the module `imports`.
-    The  `InMemoryWebApiModule` replaces the default `Http` client backend —
-    the supporting service that talks to the remote server —
-    with an  _in-memory web API alternative service_.
+    Rather than require a real API server, this example simulates communication with the remote server by adding the
+    <a href="https://github.com/angular/in-memory-web-api" target="_blank" title="In-memory Web API"><i>InMemoryWebApiModule</i></a>
+    to the module `imports`, effectively  replacing the `Http` client's XHR backend service with an in-memory alternative.
 
   +makeExcerpt(_appModuleTsVsMainTs, 'in-mem-web-api', '')