Log Message:
cxxopts: update to 3.1.1

3.1.1

Fix version number in header.

3.1.0

- Support for multiple long names for the same option (= multiple long aliases)
- Add a program() function to retrieve the program name.
- Added a .clang-format file.
- Added iterator and printing for a ParseResult.
- Cleanup exception code, add cxxopts::exceptions namespace.
- Fix arguments() having no key for options that only have a short name.