def keys(pattern = nil, secret_only = nil)
      keys = []
      each_key(pattern, secret_only) do |key|
        keys << key
      end
      keys
    end
def keys(pattern = nil, secret_only = nil)
      keys = []
      each_key(pattern, secret_only) do |key|
        keys << key
      end
      keys
    end
Returns the keys that match the +pattern+, or all if +pattern+ is nil.
 Returns only secret keys if +secret_only+ is true.