[PR-168] Remove dependency on future (#168)

Currently the python-future package is only used to provide `input`.
However, `six` is also used within the source code for python2
compatibility. Replace the usage of `future` with `six` to trim the
required dependencies.

python-future also does not provide built wheels, so removing it means
that this package and all it's dependencies can be fetched as wheels
without running any local build steps.

examples/pylink-rtt

@@ -28,7 +28,7 @@ import pylink
 import argparse
 import sys
 import time
-from builtins import input
+from six.moves import input
 
 try:
     import thread

requirements.txt

@@ -1,6 +1,5 @@
 behave == 1.2.5
 coverage == 4.4.1
-future
 psutil >= 5.2.2
 pycodestyle >= 2.3.1
 six

setup.py

@@ -261,7 +261,6 @@ def long_description():
     # Dependencies.
     install_requires=[
         'psutil >= 5.2.2',
-        'future',
         'six'
     ],