Redis sub_conn & pub_conn options

[ivanetchart]

The two options are documented but actually doesn't seems like the options are being used in the code. It was something that got removed or never implemented ?

If you agree, I can create a new PR for that.

redis_ascoltatore.rb

 *  - `sub_conn`, the optional redis connection to use for the sub and psub commands;
 *  - `pub_conn`, the optional redis connection to use for the pub command;

[mcollina]

Go ahead! ;)

[willin]

?