To sort an image's colors from darkest to lightest, you can then do:
```handlebars
{{ {{ $colorsByLuminance := sort $image.Colors "Luminance" }}
```
This uses the formula defined here: https://www.w3.org/TR/WCAG21/#dfn-relative-luminanceFixes#10450
* Add file context to minifier errors when publishing
* Misc fixes (see issues)
* Allow custom server error template in layouts/server/error.html
To get to this, this commit also cleans up and simplifies the code surrounding errors and files. This also removes the usage of `github.com/pkg/errors`, mostly because of https://github.com/pkg/errors/issues/223 -- but also because most of this is now built-in to Go.
Fixes#9852Fixes#9857Fixes#9863
