Added some advanced options

thanks for the neat tool, I like it much more than using openssl in the command line ;-)

I added a few more options that I needed.
Especially the --domain option which enables to create wildcard certificates

Don't know a lot of this stuff, but think I got it right

./etc-ca init
   --years '10'			How long until the CA certificate expires
   --organization 'etcd-ca'	CA Certificate organization
   --country 'USA'		CA Certificate country

./etc-ca new-cert
   --domain ''			Use domain instead of IP address for SAN
   --organization 'etcd-ca'	Certificate organization
   --country 'USA'		Certificate country

./etc-ca sign
   --years '10'		How long until the certificate expires