tex-gentombow{,-doc}: Add version 2020

From Atsushi Toyokura in pkgsrc-wip

This bundle provides a LaTeX package for generating
Japanese-style crop marks (called 'tombow' in Japanese) for
practical use in self-publishing. The bundle contains the
following packages: gentombow.sty: Generate crop marks (called
'tombow' in Japanese) for practical use in self-publishing. It
provides the core 'tombow' feature if not available.
pxgentombow.sty: Superseded by gentombow.sty; kept for
compatibility only. bounddvi.sty: Set papersize special to DVI
file. Can be used on LaTeX/pLaTeX/upLaTeX (with DVI output

(markd)