class type directory_name = object .. end
Directory names are also known as distinguished names. These are
    the o=foo,ou=foounit,c=country strings that are used to name
    certificates.
method name : (oid * Netasn1.Value.value) list list
This is the raw version of the DN: a sequence of relative DNs,
        and a relative DN is a set of (type,value) pairs. The types are
        things like cn, country, organization, ...
method eq_name : (oid * Netasn1.Value.value) list list
The name normalized for equality comparisons. In particular,
        PrintableString values are converted to uppercase, as well
        as emailAddress attributes. Also, the inner list is sorted by
        oid.
method string : string
The DN as string (RFC 4514)
method eq_string : string
The eq_name converted to string