…ompatibility.

Import ABC from collections.abc instead of collections for Python 3 compatibility

Fixes all but 1 test, but only under the condition that also the _convert method in Robot's Remote.py is update to automatically convert bytes to unicode whenever possible.

Without updating Robot's Remote.py 5 tests still fail.

Update test suite to match latest Robot and Python versions

- Require running it with Python 3. We want to run tests with new RF
  versions that aren't compatible with Python 2 even though
  remote server itself still supports Python 2.

- Make compatible with RF 4.0+ that don't have criticality concept
  anymore.

Use `inspect.getfullargspec` instead of the removed
`inspect.getargspec` on Python 3. Fixes robotframework#81.

- Longer timeouts avoid problems with slow interpreters
  (especially Jython on Windows).
- Verbose unit test run to see where tests possibly hang.
- Skip hanging tests with IronPython.
- Support interpreter having spaces like `py -3.8`.
- Cleanup (TRY/EXCEPT and IF/ELSE FTW!).

- Update supported versions.
- Mention that '0.0.0.0' address listens all IPv4 interfaces,
  not all interfaces. Fixes robotframework#60.