Python3: README.rst should be openned as utf-8.

Addressing:
$ /usr/bin/python3 setup.py install
Traceback (most recent call last):
  File "setup.py", line 7, in <module>
    readme = open('README.rst').read()
  File "/usr/lib64/python3.3/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position
8545: ordinal not in range(128)