Incremental release

NEW:

• Pub/Sub connection commands accept Channel instances (see #168);
• Implement new Pub/Sub MPSC (multi-producers, single-consumer) Queue --
  aioredis.pubsub.Receiver (see #176);
• Add aioredis.abc module providing abstract base classes
  defining interface for basic lib components (see #176);
• Implement Geo commands support (see #177 and #179);

FIX:

• Minor tests fixes;

MISC:

• Update examples and docs to use async/await syntax
  also keeping yield from examples for history (see #173);
• Reflow Travis CI configuration; add Python 3.6 section (see #170);
• Add AppVeyor integration to run tests on Windows (see #180);
• Update multiple development requirements;