Provide a command line flag to set additional dmenu parameters

[hashworks]

For example, this allows one to provide additional rofi opts:

tessen -d rofi --dopts="-window-title=test -monitor 0"

My use case is the following: On sway, rofi isn't able to determine the focused monitor. Thus, I need to provide that information dynamically:

rofi -show run -monitor "$(swaymsg -t get_outputs | jq '.[] | select(.focused) | select(.id) | .name')"

With this PR, I can do the same with tessen:

tessen -d rofi --dopts "-monitor $(swaymsg -t get_outputs | jq '.[] | select(.focused) | select(.id) | .name')"

[hashworks]

Fixed the format issue with shfmt -w -s -i 2 -bn -ci -sr tessen.