The main topic of this commit is that you can now index fragments (content heading identifiers) when calling `.Related`.
You can do this by:
* Configure one or more indices with type `fragments`
* The name of those index configurations maps to an (optional) front matter slice with fragment references. This allows you to link
page<->fragment and page<->page.
* This also will index all the fragments (heading identifiers) of the pages.
It's also possible to use type `fragments` indices in shortcode, e.g.:
```
{{ $related := site.RegularPages.Related .Page }}
```
But, and this is important, you need to include the shortcode using the `{{<` delimiter. Not doing so will create infinite loops and timeouts.
This commit also:
* Adds two new methods to Page: Fragments (can also be used to build ToC) and HeadingsFiltered (this is only used in Related Content with
index type `fragments` and `enableFilter` set to true.
* Consolidates all `.Related*` methods into one, which takes either a `Page` or an options map as its only argument.
* Add `context.Context` to all of the content related Page API. Turns out it wasn't strictly needed for this particular feature, but it will
soon become usefil, e.g. in #9339.
Closes#10711
Updates #9339
Updates #10725
This commit adds a .Data object (a map with `Body`, `StatusCode` etc.) to the .Err returned from `resources.GetRemote`, which means you can now do:
```
{{ with .Err }}
{{ range $k, $v := .Data }}
{{ end }}
{{ end }}
```
Fixes#9708
Introduces the Crop method for image processing which implements gift.CropToSize. Also allows a smartCrop without resizing, and updates the documentation.
Fixes#9499
In Hugo 0.90.0 we introduced remote support in `resources.Get`.
But with remote resources comes with a higher chance of failing a build (network issues, remote server down etc.).
Before this commit we always failed the build on any unexpected error.
This commit allows the user to check for any error (and potentially fall back to a default local resource):
```htmlbars
{{ $result := resources.Get "https://gohugo.io/img/hugo-logo.png" }}
{{ with $result }}
{{ if .Err }}
{{/* log the error, insert a default image etc. *}}
{{ else }}
<img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
{{ end }}
{{ end }}
```
Note that the default behaviour is still to fail the build, but we will delay that error until you start using the `Resource`.
Fixes#9529
