Error refactoring

[arkanoider]

Hi @grunch ,

putting here as an example of possible refactoring idea based on the blog article I shared on telegram:

https://sabrinajewson.org/blog/errors

I like the idea inside seems more elegant also if it's a required an effort in code and many calls to map_err when we can have a Result.

Putting here this as draft to share what could be te result, now settings.rs has some refactoring i did and results of error are now like this:

mostrod.exe -d c:\mostroSettings
Error: error reading `c:\mostroSettings\`

Caused by:
    expected an equals, found a newline at line 18 column 4 in ..\..\..\..\mostroSettings\settings.dev.toml

or

Error: error reading `H:\.mostro\`

Caused by:
    Forbidden access. (os error 5)

The approach is to avoid a big enum file and distribute errors in relative file, creating more specialized ones.

This will remove also anyhow crate.

Let me know what you think about...