documentation: Updates to support a 1.8.1 YP manual release.

Involves setting poky.ent variables, updating the manual
revision tables, and editing the mega-manual.sed file to
have the 1.8.1 string in there.

(From yocto-docs rev: 5f06e00c9bd657059433cd3487e86eccd31e5cd6)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/kernel-dev/kernel-dev.xml

@@ -61,6 +61,11 @@
                 <date>April 2015</date>
                 <revremark>Released with the Yocto Project 1.8 Release.</revremark>
             </revision>
+            <revision>
+                <revnumber>1.8.1</revnumber>
+                <date>November 2015</date>
+                <revremark>Released with the Yocto Project 1.8.1 Release.</revremark>
+            </revision>
         </revhistory>
 
     <copyright>