Splits a fraction jff

Using the continued fraction method for splitting. All information here.
Yeah, static typing is cool. (PEP 484 & PEP 526)

I didn't use typing.cast, because in doc says This returns the value unchanged, i.e. pure bla-bla-bla function.

Installing

Python 3.6

~# pip install pipenv (if you doesn't have it)
~# pipenv install  
~# python shell
~# pytest

Output:
==================== test session starts ====================
platform darwin -- Python 3.6.5, pytest-3.6.0, py-1.5.3, pluggy-0.6.0
rootdir: /bla-bla-bla/fraction, inifile:
collected 1 item

test_fraction.py .                                          [100%]

==================== 1 passed in 0.14 seconds ====================