Proposal: rename prettyerr package

[jeroenrinzema]

The prettyerr package is responsible for the construction and formatting of errors. The package supports the ability to define multiple error formats for different use cases (ex: human errors, linters...). The name prettyerr gives a wrong impression of where the package should be used for.

I would like to propose to rename the package to formatters. The Prettifier methods could be renamed to Human to indicate that the formatted errors are meant for human consumption. Future linters will be added inside this package.