Adds tests for EVAL command
Adds enable_offline_queue (see node-redis)
Supports deeply nested multi-bulk replies.

Deeply nested multi-bulk replies are used, for instance, in
SLOWLOG replies.

See this SO question:
http://stackoverflow.com/questions/15188146/nested-multi-bulk-replies-in-redis

So, we now build a tree so we can deal with replies of
arbitrary depth.
EVAL tries to do EVALSHA first.

When executing a script, tries first with EVALSHA.
If the script is not loaded, retries with the source.

This improves bandwidth for big scripts.

Also, SCRIPT commands are now supported (KILL, LOAD, FLUSH, EXISTS)
Updated README. EVAL is now supported