Errors should have the variables as properties

[jwoertink]

https://github.com/luckyframework/avram/blob/9251a965372d319977558bcbe3d0696f60aeb45e/src/avram/errors.cr#L23-L31

You should be able to access these locals as properties so that way if you need to customize this error, you can.

This is just one class, but there's a few that could benefit here as well