Warn user when importing cert with SANs that SSLMate can't handle
Add --no-install option to `sslmate import`

It prevents the key and cert files from being installed to the local
key and cert directories.
mkconfig: include recommended security settings

(Unless the --no-security option is specified.)

The recommendations come from the Mozilla Server Side TLS Guide:
https://wiki.mozilla.org/Security/Server_Side_TLS
Document mkconfig security settings in man page
Tell user about mkconfig and test after buying a cert
Properly configure default paths when running mkconfig
Version 0.6.2