Possibility to initialize ecl_smspec_node directly

[asnyv]

afaik not possible to read SMSPEC and get metadata without also reading UNSMRY (by using EclSum). See e.g: ecl_smspec_node init function

If you want to extract the union of metadata from many simulations, having to copy and process UNSMRY adds a lot of unnecessary overhead.

Would be nice to be able to make an object that only contains what is covered by ecl_smspec_node by reading a SMSPEC file directly.