Implemented MSON section parsers

Please merge. This PR implements all related MSON section parsers.
This is sort of "internal" thing of how MSON parser work. We might think of a better solution, also the name and the word "kind" is not quite right (See bellow). Please elaborate in the comment a bit on the purpose of this struct as it is not apparent (particularly the fact that it does not have to be in the interface – AST).