Write a clone of `upslog`

[Aram Peres]

man page: https://networkupstools.org/docs/man/upslog.html

upslog is a daemon that will poll a UPS at periodic intervals, fetch the variables that interest you, format them, and write them to a file.

The goal of this ticket is to write a clone, rupslog.

Note: license as GPL-3.0