HISTORY.rst causes problem with pip install on python 3.6

Using a 3.6 virtualenv, pip install breaks when installing complexity-0.9.1.

The error occurs when reading the HISTORY.rst file, with the first character of the tree diagram in the release notes for 0.4: `UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 2378: ordinal not in range(128)`

This seems to be because the content of HISTORY.rst is UTF8, but a non-binary mode `open` is expecting ASCII, and so the codec errors out.

I was able to "fix" this by hacking setup.py to read HISTORY.rst in binary mode, and decode the resulting buffer as UTF8. I *think* that'd work for 2.7 also, although I didn't try it.

See also issue #4, which appears to report a related problem with Python 2.7.

Start by inspecting setup.py where HISTORY.rst is read, then reproduce the failure in a Python 3.6 virtualenv with pip install complexity-0.9.1. Check the related issue #4 for Python 2.7 context. Done means the package installs successfully without the UnicodeDecodeError and the existing release-history content remains intact.

Written by the indexing model from the issue text.