v3.1.0

This is a minor release with some minor bug fixes and some new utility features.

The changelog for this release is

Added

• 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.

Changed

• Cleanup exception code, add cxxopts::exceptions namespace.

Bug Fixes

• Fix arguments() having no key for options that only have a short name.