Error handling improvements

This version brings multiple improvements to error handling.

There is a small breaking change though: hyprland.ValidationError is now hyprland.ErrorValidation, and it is not a custom error type anymore, instead being derived from errors.New. It means you can't cast to this error anymore, but now you can just use errors.Is or errors.As if you want to capture and treat this error in some special way.

What's Changed

• request_types: ValidationError -> ErrorValidation by @thiagokokada in #37
• request: improve error handling in RawRequest() defer by @thiagokokada in #38
• Add errcheck linter, fix issues by @thiagokokada in #39

Full Changelog: v0.2.0...v0.3.0