- added unit test
Made some changes after Christian`s review on pull request
- remove/edit comments
- BoolType and ContractType return VoidType after delete
- fixed constructor_arguments test
- fixed set to 0 when deleting variable from stack
- changed test case to test that
ExpressionStatement functions as glue between Statements and Expressions.
This way it is possible to detect when the border between statements and
expressions is crossed while walking the AST. Note that ExpressionStatement is
not the only border, almost every statement can contains expressions.