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
I will do a new rename in a minute, but my take on this now is that:
* Every site should have a hugo.toml (or yaml,json) file.
* In most simple setups, I would limit the use of the /config folder to environment specific things.
Updates usage.md to correct a small typo on line 123. Changing "When are ready to deploy your site, run:" to "When you are ready to deploy your site, run:".
* Added missing `/` in URL generator
In the example to render tags and topics, we use:
```html
<a href="{{ "tags" | absURL }}{{ . | urlize }}">
```
But this will produce links like `www.example.com/tagsTerm` where `Term` is a tag. So added the missing `/`.
* Updated the tags and topics listing code
The example previously used the old `with .Params.tags` style. Updated it to use `.GetTerms "tags"` style.
