Renew a certificate if not all names are covered by the current certificate yet.
Adds a new `--names` option to `check` that makes `check` fail if not all names are covered.
Resolves#34.
Resolves#35. Takes the value from the global config file as default argument.
If it doesn't exist, but something in the config file exists, it takes that.
If a command line argument is provided, it always takes precedence.
