Contract ({ :secret => C::SecretArg, :threshold => C::Maybe[C::ThresholdArg], :num_shares => C::Maybe[C::NumSharesArg], :identifier => C::Maybe[C::IdentifierArg], :hash_alg => C::Maybe[C::HashAlgArg], :format => C::Maybe[C::FormatArg], :padding => C::Maybe[C::Bool] }) => C::ArrayOfShares
  def self.split(opts)