Redis connection pooling

[jupenur]

I added connection pooling to the Redis client. Previously the client could only be used from a single fiber, with no way of moving it to another. That's now handled automatically by the connection pool.

[s-ludwig]

Thanks for the improvements and sorry for the late reply. I just have two minor points:

• Not sure from the way github displays the diff, but it looks like indentation uses spaces - should use tabs
• It was already commented out before, but I think line 115 should indeed also check if m_conn is still connected

[jupenur]

Uncommented. And yes, those are tabs.

[s-ludwig]

Okay, great. I'll merge.