Add signing stage to pom.xml.

In preperation for a proper release, add a plugin to the pom file to
sign everything.

pom.xml

@@ -170,6 +170,23 @@
                     </excludePackageNames>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-gpg-plugin</artifactId>
+                <version>1.6</version>
+                <executions>
+                    <execution>
+                        <id>sign-artifacts</id>
+                        <phase>verify</phase>
+                        <goals>
+                            <goal>sign</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <keyname>D16B88B9B969A4C78A4BE6C64725BF17E528FE9E</keyname>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
     <parent>