Add support for more code formatters

[nijel]

There is currently support for pep8ify, but it would be useful to support other tools in this way:

• black
• isort

[alimcmaster1]

@OrkoHunter - what would it take to support black? Mind outlining what would be involved? I might be interested in working on this.

Thanks,

Ali

[OrkoHunter]

@alimcmaster1 Thank you so much for your interest! Let me post an overview about how this can be implemented.

• User commends pep8ify on a Pull Request and the server receives the call here which calles pep8speaks.hanndlers._pep8ify.
• Here it forks the repository, creates a new branch, makes a commit and creates a pull request. It runs autopep8 by default. For this change, the formatter can be obtained from the .pep8speaks.yml config. So, let us say if scanner.formatter is set to black, then it can use black to format the code. If that key is not present in the config, then it can continue with the default autopep8.