Feature request: {{<parent}} blocks

[JoshuaWise]

The official mustache website describes {{<parent}}{{/parent}} blocks, which are basically partials, except they can contain overridable {{$block}}{{/block}} sections. As far as I can tell, this feature is missing from this package.

Reference: https://mustache.github.io/mustache.5.html#Parents

[bobthecow]

"blocks" (e.g. {{$foo}}{{/foo}}) and "parents" (e.g. {{<bar}}{{/bar}}) are part of the optional "template inheritance" spec. Many Mustache implementations don't currently implement this, as it's a more recent addition to the spec.

In this case, it was added to the Mustache spec a month after the most recent release of Mustache.js.

[JoshuaWise]

Ahh okay, then I guess it's not a bug. This issue can be recategorized as a feature request.

[solidgoldpig]

There was a previous PR for this

#473

[robinmetral]

Supporting the inheritance module in mustache.js would be amazing! This is the main thing that prevents me from using mustache in more complex projects. @janl are you open to a PR?

There was a previous PR for this

#473

That one is 9 years old and looks like it should be updated to match the spec's optional inheritance module. Might be easier to start from scratch?