Change docs links to actual file extension (.md)

See https://gerrit-review.googlesource.com/83950 for detailed context.

Change-Id: I3333f41cac05a505d49d0c7b575c069218abd67b

src/main/resources/Documentation/about.md

diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index 6be38e2..d5ac2fa 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -29,7 +29,7 @@
 The `raw` parameter cannot be used for binary files.
 
 *WARNING:* By default inline HTML blocks as well as inline HTML tags
-may be [suppressed](config.html#formatterAllowHtml) by formatters. If
+may be [suppressed](config.md#formatterAllowHtml) by formatters. If
 suppressed both will be accepted in the input but not be contained in
 the output.
 
@@ -59,8 +59,8 @@
       <a href="http://www.methods.co.nz/asciidoc/userguide.html">Aciidoc</a>
     </td>
     <td>
-      asciidoctorj: <a href="licenses.html#MIT-asciidoctor">MIT License</a><br/>
-      jruby: <a href="licenses.html#EPL1_0">Eclipse Public License 1.0</a>
+      asciidoctorj: <a href="licenses.md#MIT-asciidoctor">MIT License</a><br/>
+      jruby: <a href="licenses.md#EPL1_0">Eclipse Public License 1.0</a>
     </td>
     <td>
       <a href="http://asciidoctor.org/docs/asciidoctorj/">http://asciidoctor.org/docs/asciidoctorj/</a></br>

src/main/resources/Documentation/user.md

diff --git a/src/main/resources/Documentation/user.md b/src/main/resources/Documentation/user.md
index 5c47321..3ca869a 100644
--- a/src/main/resources/Documentation/user.md
+++ b/src/main/resources/Documentation/user.md
@@ -8,7 +8,7 @@
 
 By default the entry point to the project documentation is a
 `README.md` file in the root directory of a project. Another index file
-may be [configured](config.html#webIndexFile).
+may be [configured](config.md#webIndexFile).
 
 If a project contains the index file in its root directory then a link
 to the project documentation is displayed for it in the
@@ -70,7 +70,7 @@
 ```
 
 By default inline HTML blocks as well as inline HTML tags may be
-[suppressed](config.html#formatterAllowHtml) by formatters. If
+[suppressed](config.md#formatterAllowHtml) by formatters. If
 suppressed both will be accepted in the input but not be contained in
 the output.
 
@@ -85,7 +85,7 @@
   from which the documentation is shown, or the abbreviated ID of the
   revision if no names are found.
 
-The plugin provides several [formatters](about.html#formatters) for
+The plugin provides several [formatters](about.md#formatters) for
 different project documentation syntaxes. The formatters can be
-[configured](config.html#projectConfig) on project level and for some
-formatters the CSS can be [customized](config.html#projectCss).
+[configured](config.md#projectConfig) on project level and for some
+formatters the CSS can be [customized](config.md#projectCss).