md_eval.pl -- Provide evaluable markdown

This module adds evaluable sections to markdown cells in SWISH notebooks. Such cells are written as

```{eval}
<Prolog code>
```

 eval_dom(+DOM0, -DOM, +Options) is semidet[private]

This predicate post-processes the wiki DOM result if the DOM contains at least one eval code fragment. The evaluation is executed in a sandboxed environment, much like the Pengines infrastructure.

A code fragment is represented by a term of this shape:

pre([class(code), ext(Ext)], Text)

 md_eval(+Module, +Options, +DOM0, -DOM, +FragI0, -FragI1)[private]

 swish_provides(?Term) is nondet

True when Term describes a provided feature of the current SWISH instances. Provided Term values are:

plugin(Name)

True when Name is the name of a loaded plugin

In addition, plugins may provide additional terms by adding facts to swish_config:config(provides, Term).

 swish_has_plugin(+Name) is nondet[private]

True when Name is the name of a loaded plugin. This predicate is intended for dynamic markdown pages.