The idea behind this is to allow a config file or addon to inject
a list output filter after all the other filtering has been
performed. The existing TODOTXT_SORT_COMMAND provides a hook
for a custom filter prior to colorization and priority/context/proj
hiding; this new TODOTXT_FINAL_FILTER provides a hook for custom
filtering after the colorization and pri/con/proj hiding.
(I found this hook was needed when I wanted to trim the output to a
maximum line length.)
Note: I've added a number of tests of the list command, including
one for this new variable, as part of this change.
Signed-off-by: Emil Sit <sit@emilsit.net>
