Primary motivation is documentation, but it will also hopefully simplify the code.
Also,
* Lower case the default output format names; this is in line with the custom ones (map keys) and how
it's treated all the places. This avoids doing `stringds.EqualFold` everywhere.
Closes#10896Closes#10620
This applies two related fixes/improvements:
* The --gc now keeps empty `_resources/_gen/images` etc folders, even if empty. This should have been the behaviour
from the start.
* Also, if removal of an empty dir on Windows fails with the "used by another process" error, just ignore it for now.
Fixes#10781
This also speeds up situations where you only need the fragments/toc and not the rendered content, e.g. Related
with fragments type indexing:
```bash
name old time/op new time/op delta
RelatedSite-10 12.3ms ± 2% 10.7ms ± 1% -12.95% (p=0.029 n=4+4)
name old alloc/op new alloc/op delta
RelatedSite-10 38.6MB ± 0% 38.2MB ± 0% -1.08% (p=0.029 n=4+4)
name old allocs/op new allocs/op delta
RelatedSite-10 117k ± 0% 115k ± 0% -1.36% (p=0.029 n=4+4)
```
Fixes#10750
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
