Add a way to modify error messages about cats-parse HOT 2 CLOSED

I think this is quite related to #43

What do you think of the solution proposed there? One thing I like about avoiding opaque is that we can generally report what was expected, so you can make clearer suggestions to users (just printing the error won't work well, but you can render them nicely and in context in principle, https://github.com/johnynek/bosatsu does this, but it uses typelevel/paiges to do it, and I have been reluctant to add the dependency in this project).

from cats-parse.

That would definitely improve the situation.

If I'm understanding #43 correctly, it would allow customizing the rendering of the error based on the scope, allowing the reporter to render the whitespace in the errors above as something like "\t\n\u000b\f\r\u001c\u001d\u001e\u001f  ᠎\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2008\u2009\u200a\u2028\u2029\u205f　", which would be much easier to differentiate between the available options.

Attaching an offset to a scope could help clarify one part of the error encoding that's currently a bit unclear: what is the difference between the offset in the parent Error and the offsets contained in each Expectation?

from cats-parse.