glibmm: New API in glibmm 2.56

glibmm 2.57.1

New API in glibmm 2.56

Member Glib::ConvertError::EMBEDDED_NUL
Member Glib::DateTime::format (const Glib::ustring& format_str) const
Member Glib::ustring::compose (const ustring& fmt, const Ts&... args)
Member Glib::ustring::format (const Ts&... args)
Member Glib::VariantBase::operator!= (const VariantBase& other) const
Member Glib::VariantBase::operator== (const VariantBase& other) const