WIP: Support redis py 3.0

[maerteijn]

As I saw the "Help wanted" label for #136 here my first attempt (WIP) to fix the issues so Dramatiq works with the redis-py 3.0 package.

For as far I can see from the breaking changes the following issues have impact on dramatiq:

• The StrictRedis class has been renamed to Redis. StrictRedis will continue to exist as an alias of Redis for the forseeable future.
• The legacy Redis client class has been removed. It caused much confusion to users.
• ZADD now requires all element names/scores be specified in a single dictionary argument named mapping. This was required to allow the NX, XX, CH and INCR options to be specified.

These issues are addressed in this pull request. disptach.lua seems to work fine, however I'm not so a LUA programmer so it could be luck that it still works 😄 Will investigate later or maybe you have some hints for me

[Bogdanp]

Thanks! I'll merge this for 1.5 sometime in the next couple of months.

[Bogdanp]

Thanks again! I merged your changes with rebase (and some of my own tweaks on top) and will cut a release later today.