C++ library for generating LALR(1) parsers

 Pog is C++17 library for generating LALR(1) parsers. This library is
 header-only itself but requires RE2 library which does not come with
 header-only version. It splits definitions of parser into:
  * Declaration of tokens (regular expressions describing how the input should
    be tokenized)
  * Grammar rules over tokens from tokenization phase