Added the values package and Statement type checker (not implemented yet).
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql
modified the type checker for logical operations of boolean and string. And added some parts of the expression evaluator.
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql
Added assign to ql grammer and the lexer. Added tests for assign statment. Inserted new functionalities to expression evaluator.
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql