* Added directives recognition in SM AST.
* Moved semi-standard SM `Property` type to separate handler.
* Added `const` recognition from SM AST.
* Removed redundant `this`-as-identifier recognition.
* Removed redundant rules for abstract SM types.
* Described `CatchClause` using string syntax.
* Added support for semi-standard `range` tuple as location source.
* Added back-conversion support (to be improved).