Use UTF-8 encoding to read the README file

[suntonix]

I had trouble installing this package on a system that uses a locale without Unicode:

me@home:~$ python3 setup.py
Traceback (most recent call last):
  File "setup.py", line 93, in <module>
    LONG_DESCRIPTION = project_content('README.md')
  File "setup.py", line 77, in project_content
    out += handle.read()
  File "/usr/lib/python3.5/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 99: ordinal not in range(128)

Explicitly setting the encoding to 'utf-8' in the call to open() fixes this problem.