A line longer than 2G might overflow the size_t containing the buffer
length on 32-bit platform. Fix is to use reallocarray with second
parameter twice the size of the element to double the buffer size, since
it will error out if there was an overflow.
b commonly corresponds to Page Up, and f is added to match.
j and k for lines, ^F and ^B for pages, and g and G for home/end are from vi.
C-n and C-p for lines and C-v and M-v for pages are from Emacs.
< and > for home/end allow using Emacs M-< and M->, tho they are from less(1).
I hereby relicense all my work on Sortix under the ISC license as below.
All Sortix contributions by other people are already under this license,
are not substantial enough to be copyrightable, or have been removed.
All imported code from other projects is compatible with this license.
All GPL licensed code from other projects had previously been removed.
Copyright 2011-2016 Jonas 'Sortie' Termansen and contributors.
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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