It seems the current code doesn't allow for removing the email address
from the contact field. This fixes that. This only removes the email
address if an explicit empty email address is specified on the command
line or in the account.conf file. If it is left unspecified on the
command line it still just uses whatever was configured in the
account.conf.
Default of a zone might be high, which is annoying when testing
with the ACME staging API. I think setting the TTL to 0 makes sense
as acme.sh is the only one checking this, so having an always up
to date response seems desirable.
