Refine the syntax of separation logic:
- VariableExpression is deprecated, Variable is used instead of VaraibleExpression.
- EqNullTerm, NEqNullTerm, EqTerm, NEqTerm are deprecated. They will be replaced by ComparisonTerm.
- Add NullExpression
- Optimizing the alias container using HashMap instead of LinkList<LinkedList>. Hopefully it will be faster.
- Change also the antlr grammar .g4 file.
- All unit tests are OK.