Feature request: Compact output/Configurable output format

[donpdonp]

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.