DATAREDIS-336 - Copy styles to output dir.

Upgraded to Asciidoctor 1.5.0. We now cheat on Gradle docbook-reference-plugin by directly copying files to reference work dir to bypass expanding files. Create an empty source folder so that the plugin does not fail.

Original pull request: #94.

src/asciidoc/appendix/introduction.adoc

@@ -1,5 +1,5 @@
 [float]
-= Document structure
+= Appendix Document structure
 
 Various appendixes outside the reference documentation.
 

src/asciidoc/reference/redis.adoc

@@ -177,6 +177,8 @@ public RedisConnectionFactory jedisConnectionFactory() {
 } 
 ----
 
+Sometimes direct interaction with the one of the Sentinels is required. Using `RedisConnectionFactory.getSentinelConnection()` or `RedisConnection.getSentinelCommands()` gives you access to the first active Sentinel configured.
+
 [[redis:template]]
 == Working with Objects through RedisTemplate