New standard package: a redis client

I have added a default client for redis as See there for details. I was first considering to add this as a normal pack, but eventually I considered it better to add it to the base system as the library is fairly small, will eventually use a bit of C code to speedup reading Redis replies (and foreign code is always a bit tricky to distribute). I also think that using redis to share storage and exchange messages with other processes is so simple that it is worth adding as a core component.

The contains some stuff that still needs to be done. I follow the traditional path: release early and release often. This is the time if you have wishes that require some rethinking of the API or design.