Add new utils::strfind() function and update mini-regex code

[akohlmey]

Summary

This updates the mini-regex code in the utils namespace to the current version with a few portability and bug fixes and indication of the length of a match. The latter is needed for the new utils::strfind() function that may replace the use of (not yet) fully portable use of std::regex across our range of supported machines.

Related Issue(s)

Needed for PR #2625

Author(s)

Axel Kohlmeyer, Temple U

Licensing

By submitting this pull request, I agree, that my contribution will be included in LAMMPS and redistributed under either the GNU General Public License version 2 (GPL v2) or the GNU Lesser General Public License version 2.1 (LGPL v2.1).

Backward Compatibility

No known issues. Existing unit tests for utils::strmatch() pass.

Post Submission Checklist

• The feature or features in this pull request is complete
• Licensing information is complete
• Corresponding author information is complete
• The source code follows the LAMMPS formatting guidelines
• Suitable new documentation files and/or updates to the existing docs are included
• The added/updated documentation is integrated and tested with the documentation build system
• The feature has been verified to work with the conventional build system
• The feature has been verified to work with the CMake based build system
• Suitable tests have been added to the unittest tree.

Further Information, Files, and Links

https://github.com/kokke/tiny-regex-c