Let setup.py know that at least Python 3.6 is required

[asgeroverby]

Python 2 and Python < 3.6 were dropped in favor of f-strings.

setup.py updated to reflect this.

The bincopy > 17 does not work on python 3.5 after f-strings were introduced.

pi@raspbian-stretch:~ $ python3 --version
Python 3.5.3
pi@raspbian-stretch:~ $ python3 -m bincopy --version
Traceback (most recent call last):
  File "/usr/lib/python3.5/runpy.py", line 183, in _run_module_as_main
    mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
  File "/usr/lib/python3.5/runpy.py", line 153, in _get_module_details
    code = loader.get_code(mod_name)
  File "<frozen importlib._bootstrap_external>", line 775, in get_code
  File "<frozen importlib._bootstrap_external>", line 735, in source_to_code
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "/home/pi/.local/lib/python3.5/site-packages/bincopy.py", line 84
    line = f'{size + 2 + 1:02X}{address:04X}'
                                            ^
SyntaxError: invalid syntax
pi@raspbian-stretch:~ $ python3 -m pip show bincopy
Name: bincopy
Version: 17.8.0
Summary: Mangling of various file formats that conveys binary information (Motorola S-Record, Intel HEX and binary files).
Home-page: https://github.com/eerimoq/bincopy
Author: Erik Moqvist
Author-email: erik.moqvist@gmail.com
License: MIT
Location: /home/pi/.local/lib/python3.5/site-packages
Requires: argparse-addons, humanfriendly

Workaround for python 3.5 and friends, install bincopy < 17

pi@raspbian-stretch:~ $ python3 -m pip install --upgrade bincopy==16.10
Collecting bincopy==16.10
  Downloading https://files.pythonhosted.org/packages/0a/44/ef4cab96d23323d28133e44e66a0930cbf4a346dcce3bcbf70a96a64f17a/bincopy-16.10.0-py2.py3-none-any.whl
Collecting humanfriendly (from bincopy==16.10)
  Using cached https://files.pythonhosted.org/packages/8e/2d/2f1b0a780b8c948c06c74c8c80e68ac354da52397ba432a1c5ac1923c3af/humanfriendly-8.2-py2.py3-none-any.whl
Installing collected packages: humanfriendly, bincopy
Successfully installed bincopy-17.8.0 humanfriendly-8.2
# Test
pi@raspbian-stretch:~ $ python3 -m bincopy --version
16.10.0

[coveralls]

Coverage remained the same at 96.316% when pulling cd79751 on asgeroverby:master into 09e2f97 on eerimoq:master.