Generate util javadoc.

When we implement the javadoc fetcher, we'll new get a separate
util doc as well.

DMDirc/Util#3

circle.yml

@@ -21,7 +21,7 @@ test:
   override:
     - >
       if [ -n "${BUILD_JAVADOC}" ]; then
-        ./gradlew --stacktrace packageJavadoc;
+        ./gradlew --stacktrace util:javadocJar packageJavadoc;
       elif [ -n "${BUILD_PMD}" ]; then
         ./gradlew --stacktrace pmdMain;
       else