Proposal: error types

[ehazlett]

This would add support for error types instead of return fmt.Errorf everywhere.

Refs #553

[nathanleclaire]

I think this is more of a "We need a coding style guide" than a specific issue which we can point at as definitively solved. I do agree strongly though.

[thaJeztah]

@ehazlett @nathanleclaire not sure if this is the same thing, but you might be interested in the work @duglin and @stevvooe did here; distribution/distribution#548

[nathanleclaire]

Nice callout @thaJeztah ; noted

[stevvooe]

@thaJeztah The errcode package is targeted at API-level errors. We should start using it for any errors that may cross an http/rpc (and maybe cli) boundary.

@nathanleclaire @ehazlett We're still experimenting with the API, but Machine might want to explore use of the package.

[thaJeztah]

@stevvooe yup, I was aware of that (API / http); I thought it might be interesting (for inspiration). Thanks for adding your thoughts 👍