3.1.10 CRL objects
CRL objects have the following methods:
Add a Revoked object to the CRL, by value not reference.
- export(cert, key[, type=FILETYPE_PEM][, days=100])
Use cert and key to sign the CRL and return the CRL as a string.
days is the number of days before the next CRL is due.
Return a tuple of Revoked objects, by value not reference.