add black -c "code"

[JelleZijlstra]

Useful as a way to quickly try out what Black does on a chunk of code. A -c option with similar behavior is also in mypy and python itself.

[coveralls]

Pull Request Test Coverage Report for Build 975

• 2 of 4 (50.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 95.894%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
black.py	2	4	50.0%

Files with Coverage Reduction	New Missed Lines	%
black.py	1	94.7%

Totals
Change from base Build 966:	-0.03%
Covered Lines:	3013
Relevant Lines:	3142

---

💛 - Coveralls

[zsol]

Personally, I use echo code | black - for this, but I'm not against this option. Can we rename the long option to --code though?

[JelleZijlstra]

I used --command because that's what mypy uses as the long form, but --code does make more sense. I'll make the change.