Log Message:
re2c: update to 3.1.

3.1 (2023-07-19)
~~~~~~~~~~~~~~~~

- Added capturing groups with leftmost greedy semantics:

  + Enabled with ``--leftmost-captures`` option or ``re2c:leftmost_captures``
    configuration

- Added non-capturing groups:

  + Added new syntax ``(! ...)`` for non-capturing groups

  + Added the ability to flip defaults: make ``(...)`` capturing and ``(! ...)``
    non-capturing with ``--invert-captures`` option or ``re2c:invert_captures``
    configuration

- Regenerated Unicode include header to support a newer standard

- Published TDFA paper: https://arxiv.org/abs/2206.01398, co-authored with
  Angelo Borsotti

- Removed experimental algorithms that are superseded by TDFA(1) and
  generally less efficient:

  + Removed staDFA algorithm and deprecated ``--stadfa`` option

  + Removed TDFA(0) algorithm and deprecated ``--no-lookahead`` option

  + (libre2c) Removed backward-matching algorithm

  + (libre2c) Removed Kuklewicz POSIX disambiguation algorithm

  + (libre2c) Removed GTOP shortest path finding algorithm

- Bug fixes:

  + Fixed parsing of raw UTF-8 characters in Flex compatibility mode

  + Added header file to the dependencies generated with ``--depfile`` option

  + Fixed stack overflow on large regular expressions by rewriting recursive
    functions in iterative form
    and limited stack to 256K on GithubActions CI

- Build system:

  + Added minimal http://bazel.build integration

  + Added configure option ``--enable-parsers`` that regenerates bison parsers

  + Added CMake option ``RE2C_REBUILD_PARSERS``

  + With CMake, fixed documentation generation on Windows.

- Codebase improvements:

  + Moved the entire codebase to C++11.
  + Added uniform error handling (return codes are now properly checked and
    returned to the caller).
  + Reorganized codegen subsystem in four well-defined phases (analyze,
    generate, fixup, render) and separated codegen from parsing phase.
  + Improved memory allocation by using slab allocators instead of global free
    lists.
  + Moved to pure API for bison parsers.
  + Unified code style.

- Testing:

  + Added ``--verbose`` flag to run_tests.py and suppressed verbose output by
    default.
  + Multiple improvements of continuous testing with GithubActions.