Add support for human friendly duration formatting

[jbsmith7741]

This is a proposal for issue #55 by adding a new humanize.Duration(format string, d time.Duration) function.
supports year, month (30 days), week, day, hour, minute and seconds. zero values fields are not populated and times are broken down by the requested formats. Examples are in tests

[alexykot]

Any chance to get this merged? I need this function as well, but we'll have to maintain a fork until this PR is merged.

[sheldonhull]

Bump. This would be a nice humanize feature I've missed from other languages. Duration for stop watch type output being human friendly would be pretty nifty.

[mooijtech]

Would be nice to have this, 2023 now, no right to complain I could do it myself.
You can get a time.Time from a Duration like so: endTime := time.Now().Add(-time.Since(startTime))
Nice library.