Polyswarm-client

* **Fix** - function name corrections that were missed in rc2
* **Fix** - remove awaits added in rc2 that don't belong

* **Fix** - duplicate bounty event handing
* **Fix** - enhance log messages with more useful content
* **Feature** - allow overriding API key per request
* **Fix** - code cleanup and formatting; enhance events class to include block_number and txhash as function args

* **Fix** - corrected minimum python3 version

Leading up to our PolySwarm 1.0 release, we reset the numbering to 1.0 with release candidates.

* **Feature** - This is the first release published to PyPi.

* `AbstractArbiter.scan()` and `AbstractMicroengine.scan()` will now raise an exception if it
has not been overridden by a sub-class and the subclass did not provide a scanner to the constructor.
* `AbstractAmbassador.next_bounty()` will now raise an exception if not overridden by sub-class.

**Ambassadors**

from polyswarmclient.ambassador import Ambassador
class CustomAmbassador(Ambassador):
Ambassador implementation here


**Arbiters**

from polyswarmclient.arbiter import Arbiter
class CustomArbiter(Arbiter):
Arbiter implementation here


**Microengines**

from polyswarmclient.microengine import Microengine
class CustomMicroengine(Microengine):
Microengine implementation here