Use utf-8 when reading README.md in setup.py

[alexey-sveshnikov]

Hello.

Here is a small patch which sets encoding to UTF-8 in readme.md reading in setup.py.

On pre-3.7 environments the default encoding may be different than UTF-8. AFAIK that's the case when the system locale is not set. I'm getting UnicodeDecodeError on installing rsa in clean Ubuntu 18.04 environment in Docker.

UTF-8 mode in open as well as using io.open is the recommended by pip/pypi authors practice. I used pypi sample projects as a reference (https://github.com/pypa/sampleproject/blob/master/setup.py).

[coveralls]

Coverage remained the same at 88.838% when pulling fb552c1 on alexey-sveshnikov:master into 368a31f on sybrenstuvel:master.

[jgehrcke]

This needs to be merged. Installing from the tarball is otherwise broken on many Linux systems. During setup.py install:

    Traceback (most recent call last):
[...]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 898: ordinal not in range(128)

[sybrenstuvel]

Thanks for the pull request! I've applied your changes (0eaeead) with a few minor changes:

• Removed the added 'r' argument to open(), as it's superfluous and doesn't have anything to do with the actual issue addressed in this PR.
• Copied the comment about importing io.open from the reference project you linked. I think the comment is good to keep, as it'll get relevant relatively soon when we drop Python 2 support.