Renamed BinaryTree to Binary
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql
Made the visitor type independent
added typeOf methods for expressions
Added compatibility of types
typeEnvironment gets filled, added typecheck for Add
added method bodies for visiting statements
Implemented type checking for expressions
Updated readme
Made fields in ASTNodes final
Added support for strings and made sure all relevant errors gets printed
Defined parsing BooleanLiterals in the grammar
Splitted ASTNodeVisitor into ExprVisitor and StatementVisitor
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql