improvements for annotate-output

[Daniele Pizzolli]

Hello devscripts developers,

I made some (tested) improvements to annotate-output:

- annotate-output: Add switch to show relative time
- Add microsecond support
- Add line relative time output
- Switching to dash make the script twice fast!
- Show default FORMAT value in the help

Everything is at:

https://github.com/dancn/devscripts/commits/relative

I did not found a contributor guide.  The upstream is no more a valid
link.  Opening a bug report for each patch seems a bit cumbersome.

Feel free to merge the patches as they are, if not please let me know
the best way for get the code merged.

Best,
Daniele