title: Change configuration of Python linter and fixer with ALE (nvim plugin)
body: <p>I use ALE to manage my linting (with flake8) and code formatting (with black).
  One annoying incompatibility between flake8 and black is that flake8 gives an error when a line has more than 80 characters, while black only corrects lines with more than 88 characters.</p>
  <p>So I would like to change flake8's line length to 88 characters, or change black's line length to 80 characters.</p>
  <p>Notice that I do not have flake8 installed independently from ALE, but I do have black installed independently from ALE.</p>