v0.6.1

- Use `asyncio.isfuture()` directly.

- Use `asyncio._set_running_loop()` and `_get_running_loop()`
  introduced in Python 3.6. This enables new behaviour of
  asyncio.get_event_loop().

- Fix `loop.create_server()`, `loop.create_connection()`,
  `loop.create_datagram_endpoint()`, and
  `loop.connect_accepted_socket()` to accept only socket
  kinds they support.  So `create_server()` will raise a
  ValueError if it receives an `AF_UNIX` socket. This is
  how asyncio will behave in Python 3.6 and in the next
  bugfix release of 3.5.

- Fix `loop.create_unix_server()` and
  `loop.create_unix_connection()` to correctly check for
  `SOCK_STREAM` on Linux, where socket type is a bit mask.

- Rework the build infrastructure, moving all logic from
  the Makefile to setup.py.