more: make page and arrow up/down to update view

more: make page and arrow up/down to update view

Aim was to introduce page and arrow up/down keys to more(1), but that
also required merging colon_command() and more_key_command() functions.

The more_key_commands enum is pointless from computers point of view.
The command identification performed in read_command() inline with
more_key_command() execution -- but that would be hard for humans, and
source code ought to serve both parties.

Reference: https://github.com/karelzak/util-linux/pull/1003
Signed-off-by: Sami Kerola <kerolasa@iki.fi>