Feature. Support of complex meta structures

Feature. Support of complex meta structures

Add support in *unwrap_c* for support of the structure: *MetaList*
with 2 x *MetaMap* with keys pointing to *MetaInlines*:

    ---
    references:
     - id: refone
       title: Ref-MetaInlines-in-MetaList
     - id: reftwo
       title: Ref-MetaInlines-in-MetaList
    ...

Actually it sounds complex but this fix should also be needed for the
simpler example of *MetaMap* with keys pointing at *MetaInlines*:

    ---
    experiment:
     key_first: Värde
     key_second: värde
    ...