Add fancy errors

[FireIsGood]

Fixes #142, maybe #124?

Adds colored errors, mostly to clean up how the offline error is displayed. These do not apply to Clap errors.

Since this adds color_eyre and errors are always returned, the new error parsing may be able to replace the entire error module. I have decided not to do that to make fewer changes for this pull request.

This adds color_eyre and thiserror.

Before:

After:

[nelsonjchen]

Hmm, I never claimed to make this tool a library, and reluctantly made some of this available to be used as such. I wonder if this breaks anything for those users.

[FireIsGood]

Technically yes.

This changes the return types of some of the public functions from Result<Response, SpeedTestError> to color_eyre::Result<Response>, which may break match statements.

The return types are mostly changed so you can get a better stack trace and suggestions in a reasonable place, however you can easily just revert the return types since the thiserror change makes your error::SpeedTestError variants have the Error trait. This means that they will automatically convert into the color_eyre type in the main function, but doesn't allow the .suggestion() for turning on the internet.

You could consider this a breaking change and then update the major version or change the return types back.

[nelsonjchen]

I'll need to think on this for a bit. I'll be honest, I wrote this a long time ago and I haven't kept up with the zeitgeist for error crate stuff. Even this project doesn't seem to build correctly at the moment in some PRs.