Problem metadata

By "metadata" we mean all extra data of a problem, that are not directly included in the statement / solution / answer. DGS expects to find those in an accompanying meta.yaml file, with a future option of parsing the YAML front matter (though this breaks the hierarchy a bit).

The actual format is somewhat ambiguous and depends on the module. For instance, for seminar we may want to store the maximum number of points that can be awarded, author's names, tags for categorizing the problems and so on.

Since 5.0 a universal templating context is available as values.

values:
    a: 5
    c: 1.453e-19
    name: 'Michelle'
    gforce:
        value: 9.80665
        unit: '\\metre\\per\\second\\squared'