Incremental release

• create_pool() minsize default value changed to 1;
• Fixed cancellation of wait_closed
  (see #118);
• Fixed time() convertion to float
  (see #126);
• Fixed hmset() method to return bool instead of b'OK'
  (see #126);
• Fixed multi/exec + watch issue (changed watch variable was causing
  tr.execute() to fail)
  (see #121);
• Replace asyncio.Future uses with utility method
  (get ready to Python 3.5.2 loop.create_future());
• Tests switched from unittest to pytest (see #126);
• Documentation updates;