Input and output changes

[f-froehlich]

Now you can specify time units (days (d), hours (h), minutes (m), seconds (s), percent (%)) for warning and critical bounds. If no unit is given default unit is percent due compatibility reasons. Changing default values to 10d (warning) and 5d (critical). Output remaining time in human readable format (d h m s) and percentage Output expiring at time in human readable format e.g. WARNING: DNSSEC signature for [DOMAIN] is short before expiration! (8d 11h 7m 40s / 28% remaining; expire at So 23 Aug 2020 18:55:00 UTC) | sig_lifetime=731260 sig_lifetime_percentage=28%;864000;432000

[mrimann]

Thanks for your contribution! By reading this looks fine. I'd like to test that before merging.