Use standard as the formatter

[sadasant]

Standard provides an API which might allow us to format all the output code with standard by default (we'll make sure we provide an optional parameter with the formatting function, so users can use their own). However, standard uses the file system API in their lintText and lintTextSync functions, which makes our unit tests fail, since we need to mock the fs API.

I opened an issue in the standard repo asking if we could optionally disallow lintText and lintTextSync to interact with the file system api: standard/standard#904

Let's see what happens!