Handle extras

[tyilo]

See https://packaging.python.org/specifications/entry-points/

Trying to install black's wheel with python-install, will produce the binary blackd with the following contents:

#!/usr/bin/python
# -*- coding: utf-8 -*-
import re
import sys
from blackd import patched_main [d]
if __name__ == "__main__":
    sys.argv[0] = re.sub(r"(-script\.pyw|\.exe)?$", "", sys.argv[0])
    sys.exit(patched_main [d]())

which of course doesn't work. python-install should not include the [d] in the file.

This is the contents of entry_points.txt for black's wheel:

[console_scripts]
black = black:patched_main
black-primer = black_primer.cli:main
blackd = blackd:patched_main [d]