Existing users should delete the old virtual environment and the old
binary link.
# rm -r /usr/local/env/tarsnapper
# rm /usr/local/bin/tarsnapper
Closes#82
Assuming the user is running Borg hourly on more or less the same
directories, it probably makes sense to give the Tarsnap timer a random
delay so that we don't end up running both at the same time and saturate
available bandwidth.
The default period is set to daily, so this doesn't change anything for
existing users -- except that now we default to only executing on AC
power. If existing users want to match the previous behavior they should
set `tarsnapper.ac_power` to `false`.
