setup.py not python2 compatible

[atward]

$ python --version
Python 2.7.15rc1
$ python setup.py 
Traceback (most recent call last):
  File "setup.py", line 12, in <module>
    long_description = open('README.rst', encoding = 'utf8').read(),
TypeError: 'encoding' is an invalid keyword argument for this function

encoding is not valid to open() in python2.

[atward]

Relates #22