Feature request: Compact output/Configurable output format

I've just started using the numbat CLI and one thing that is bothersome is the unnecessary blank lines in every output. Efficient use of whitespace is important as I often want to see the last few calculations. I've tried `pretty-print = "never"` and that stops the formula from being re-printed, but there is still leading and trailing blank lines that waste valuable screen real estate. A setting like pretty-print "compact" would make numbat easier to use, or even better, `pretty-print-format = "%{answer}"` so that the output is easily configurable, with the default being something like `pretty-print-format = "\n%{input}\n%{answer}\n"` to mimic the current output.