v1.0.0

• SemVer v1.0.0 release:
  Commitment to long-term API stability
  Guaranteed functionality on GNU platforms
  Support for other platforms is best-effort
  All tests passing on glibc, musl, OpenBSD, FreeBSD, macOS, and Haiku
• Updates:
  Compile-time guarantee: no two options in the same parser can share the
  same shortopt or the same longopt. This is done via static_assert
  Added operator+ and operator+= to OptionSequence, allowing users to
  combine multiple OptionSequences into one (e.g. for repeated parsing)