Strongly typed AST: Model Interface for statement.
Strongly Typed AST: ported PEG Syntax Tree DSL

from Java and create a new gramar class to start the migration.
Strongly Typed AST: rename package of model interfaces.
Strongly Typed AST: remove useless code.
Strongly Typed AST: Migrate EMPTY_STATEMENT rule.

Add the necessary logic to migrate the rule.
Strongly Typed AST: Small refactor for readability.
Remove mistake introduced in previous commit

f351ec726edeebf4b6d79984042fe588743d132d
Small refactor.
Rmove useless code.
Remove useless code.
Strongly Typed ASTL: add test for empty statement.
Strongly typed AST: add test to check the shape of the constructed strongly typed AST