Screenfetch uptime fmt

Created by: pi-pi3

screenfetch used to output unformatted uptime, i.e. 180s instead of the expected 3m. This commit adds basic formatting.

The formatting string is as follows: "{}d {}h {}m {}s"

Example output: 2d 11h 6m 37s

External crates were avoided. Better formatting (e.g including years) could be achieved when using external crates