Der default values

DER encoder should not include values that are equual to defaults.

Ref http://luca.ntop.org/Teaching/Appunti/asn1.html:

    DER encoding. Constructed. Contents octets are the same as the BER
    encoding, except that if the value of a component with the DEFAULT
    qualifier is the default value, the encoding of that component is not
    included in the contents octets.
So what about `result.join()`? I think it should be avoided in general non-default case. Also, I guess you may avoid it if the default value is a JS-primitive and could be checked without encoding it.