Yantra parser generator for C++ builds full AST before semantic walk

Yantra is a new LALR(1) parser generator for C++ that produces a lexer, parser, and AST walker from a single grammar specification. Unlike traditional tools like Yacc or Bison, it constructs the entire abstract syntax tree first before performing a separate, top-down walking pass to execute semantic actions. This design allows parent rule actions to run before their children are visited and enables multiple walkers from one grammar, such as for different output languages. The tool is currently at version 0.5.1, is MIT licensed, and is developed by a single maintainer who acknowledges it is in an early stage.