Support classes

[Maxcode123]

Currently there is no support for classes in classic programs.

1. In src/syntax/ast/nodes.h populate the class-related classes with the appropriate arguments (see grammar file, classical.y).
2. Implement the build methods of the builder (src/syntax/ast/builder.cpp).
3. Write unit tests for the builder methods (tests/unit/ast/test_builder.cpp)
4. Call builder on production rule actions (classical.y)
5. Write integration tests for the parser (tests/integration/syntax/test_parser.cpp)