Improve pipelines

[Grokzen]

There is alot of work that needs to be done to make pipelines work at the same level as the normal client.

• Work to unblock the basic commands that is currently blocked (mget, mset etc...)
• Take another look at NYI commands like immediate_execute_command & _execute_transaction to see if they can be implemented.
• Split send_cluster_commands into smaller parts that can be reused more easily.

[Grokzen]

Good discussion on google groups about how pipelines could be implemented in a cluster lib https://groups.google.com/forum/?hl=sv#!topic/redis-db/4I0ELYnf3bk

[Grokzen]

Closing this in favor for other/newer issues.