Support more listings (a la {!modules:..})

[xvw]

When writing manuals in .mld files, the {!modules:...} directive is very useful and I think it would be really handy to support more listing directives, to encourage writing manuals in mld that support references (and code block execution via mdx).

Here is a list of guidelines that I would find potentially useful (but there are probably others).
Ideally, the "title" of the item listed would be a link to the resource.

• {!type:...} which would display a type and the first paragraph of its documentation block (which would introduce a notion of synopsis in the documentation blocks attached to types). This primitive is useful because, for example, in a textbook, it makes it easy to list the different types used to solve a particular problem. ie: "For this task, we will essentially be using the following types: [newline] {!types: Foo.t Bar.t}"

• {!values:...} (or maybe {!vals:...}) which will display a list of values with their types and the first paragraph of their documentation block (also introducing a notion of synopsis for values, so that, for example, examples of how the function is used are not imported). I think this primitive is useful because, a bit like types, it allows you to synthesise the functions you're going to use to solve a specific task.

• {!pages:...} which simplifies the generalisation of summaries/tables of contents and which would probably use the first paragraph after heading-0 as the synopsis (the link is required here)

• {!modules-types:...}: directive, which would have the same form as the {!modules:...}, but for module-types and offering the same advantages as the modules (and types).