Filter SymbolTable output, removing C function symbols

This output is just for debugging purpose right now, it more convenient to just
print data file variables during this early development

src/language/SymbolTable.hpp

@@ -171,8 +171,10 @@ class SymbolTable
   {
     os << "-- Symbol table state -- parent : " << symbol_table.m_parent_table.get() << "\n";
     for (auto i_symbol : symbol_table.m_symbol_list) {
+      if (i_symbol.attributes().dataType() != ASTNodeDataType::c_function_t) {
         os << ' ' << i_symbol.name() << ": " << std::boolalpha << i_symbol.attributes() << '\n';
       }
+    }
     os << "------------------------\n";
     return os;
   }