Bug#910280: pandoc: Please reduce the binary size

[John MacFarlane <jgm@berkeley.edu>]

I'm happy to leave this issue up to the Debian
maintainer, since the upx compression would need to
be done in the packaging process and doesn't involve
upstream.

I tested upx compression (with --best --ultra-brute)
on macOS.  Time for 'pandoc --version' went from 0.031s
without compression to 0.756s with compression.  This
is potentially an issue for some users of pandoc
(particularly people who shell out to pandoc to
convert small bits of text).  Offering a compressed
version as an option sounds like a good idea.