Add a --single-quotes option to prefer single quotes

[davvid]

Now there are no excuses not to use black.
Fixes #594

[hugovk]

(I find double quotes easier to type on my keyboard layout, but here's some typos)

[ambv]

Thank you for your contribution but we won't be adding this to Black.

[richardARPANET]

Support for this has been added to https://github.com/odwyersoftware/brunette 👍

[rspadim]

Could the brunette --single-quotes be imported to black?

[y4rr]

Is there any explanation as to why this option not being added?

Your main page says,

Black is the uncompromising Python code formatter. By using it, you agree to cede control over minutiae of hand-formatting. In return, Black gives you speed, determinism, and freedom from pycodestyle nagging about formatting. You will save time and mental energy for more important matters.

Actually, after using your tool, I don't have any time and mental energy left at all, because I use single quotes everywhere, as they are easier to type on my keyboard.

[harahu]

Actually, after using your tool, I don't have any time and mental energy left at all, because I use single quotes everywhere, as they are easier to type on my keyboard.

Not sure I understand why you feel this is an issue, @y4rr. After all, since black will gladly swap out your quotes, there's nothing stopping you from continuing to type single quotes. Nobody is forcing you to type double quotes.

[manulera]

This feels really strange. Why not allow maintainers to harmonise string quotes to single if they want to do so? Really sad to see that a working implementation was discarded on the basis of what seems to be personal preference of the lead maintainer.