Importing current git tag with python version 3

[micah-prime]

With python 3, the current method for getting the current git tag using subrpocess.check_output returns a byte string. This can be fixed with another option in the command.

[scotthavens]

This appears to still be a problem. The commit string in the output files is not correct, both in the tag value or git hash

[jomey]

Another case for setuptools_scm?

[scotthavens]

That's what I was thinking.

The important thing though is we're getting the git hash if we're in a repo so we'd want to use the scheme that has the commit hash.

[scotthavens]

Fixed with #170