Add support for yapf formatter

[Spenhouet]

The example config in the README shows "isort.args": ["--profile", "black"] but we are using yapf as formatter.
I tried setting "yapf" here but then isort throws this error:

isort.exceptions.ProfileDoesNotExist: Specified profile of yapf does not exist. Available profiles: black,django,pycharm,google,open_stack,plone,attrs,hug,wemake,appnexus.

From this I take it that yapf is not yet supported.
I hope this can be added.

[karthiknadig]

The extension is a wrapper around isort pyhton library. When you pass those isort.args they are beeing passed to the isort tool. think python -m isort --profile yapf. So, you should be filing this as a feature request on isort here https://github.com/pycqa/isort

[karthiknadig]

Looks like there is google can you try with that for profile:

--profile PROFILE     Base profile type to use for configuration. Profiles include: black, django, pycharm, google, open_stack,  
                        plone, attrs, hug, wemake, appnexus. As well as any shared profiles.

[Spenhouet]

Thanks for the hint. I just saw that myself and also found this thread arguing about if this is actually correct: PyCQA/isort#1486
It does format imports differently to how we are used to from yapf but I can't say if it's incorrect or not.

I will raise further issues on that with isort if necessary.