1.3.2

Changes:

• Make .begin and .end methods lifetimebound.
• Remove requirement of std::is_copy_constructible_v<T> in .take_if method.
• Fix non-constexpr default/opt::none_t constructors in opt::option.
• Fix compile error when using operator=(const option<U>&) in opt::option.
• Remove option_fwd.hpp inline code from option.hpp.
• Add size optimization for std::complex.
• Add opt::as_option function.
• Change the return type of opt::from_nullable to opt::option<T&>.
• Make opt::flatten sometimes return reference options to make it more efficient.
• Make .inspect method invoke fn with rvalue references and only return *this lvalue reference.