And also adjust the graph width calculation to do a better job when the
largest item is smaller than the number of columns used for the graph,
which would previously draw either nothing (if size = 0) or a full bar
(if size > 0).

Fixes #172.

Fixes #181, now also for Zig.

Fixes #185

Fixes #183

I'm tagging this as a "stable" 2.0 release because the 2.0-beta#
numbering will get confusing when I'm working on new features and fixes.
It's still only usable for people who can use the particular Zig version
that's required (0.9.0 currently) and it will certainly break on
different Zig versions. But once you have a working binary for a
supported arch, it's perfectly stable.

...by making sure that Context.parents is properly initialized to null
when not scanning to RAM.

Fixes #179.

Port of 96a92319

Bit pointless to make these options nullable when you never assign null
to them.

Introduced in 53d3e4c1

Not going to bloat the help output with all those settings...

Saves about 15k on the binary size. It does allocate a bit more, but it
also frees the memory this time.

+ reorder manpage a bit, since the scan options tend to be more relevant
than all those UI options.

Again, these are mainly useful with a config file.

Might as well keep it. The quick-config menu popup idea can always be
implemented later on, we're not running out of keys quite yet.

The --enable-* options also work for imported files, this fixes #120.

Most other options are not super useful on its own, but these will be
useful when there's a config file.

That was an oversight. Especially useless when there's no option to
disable -x.

Same thing as commit 376aad0d in the C
version.

As aluded to in the previous commit. This approach keeps track of hard
links information much the same way as ncdu 1.16, with the main
difference being that the actual /counting/ of hard link sizes is
deferred until the scan is complete, thus allowing the use of a more
efficient algorithm and amortizing the counting costs.

As an additional benefit, the links listing in the information window
now doesn't need a full scan through the in-memory tree anymore.

A few memory usage benchmarks:

              1.16  2.0-beta1  this commit
root:          429        162          164
backup:       3969       1686         1601
many links:    155        194          106
many links2*:  155        602          106

(I'm surprised my backup dir had enough hard links for this to be an
improvement)
(* this is the same as the "many links" benchmarks, but with a few
parent directories added to increase the tree depth. 2.0-beta1 doesn't
like that at all)

Performance-wise, refresh and delete operations can still be improved a
bit.

While this simplifies the code a bit, it's a regression in the sense
that it increases memory use.

This commit is yak shaving for another hard link counting approach I'd
like to try out, which should be a *LOT* less memory hungry compared to
the current approach. Even though it does, indeed, add an extra cost of
these parent node pointers.

It's a bit ugly, but appears to work. I've not tested the 32bit arm
version, but the others run.

The static binaries are about twice as large as the ncdu 1.x
counterparts.

I had planned to checkout out async functions here so I could avoid
recursing onto the stack alltogether, but it's still unclear to me how
to safely call into libc from async functions so let's wait for all that
to get fleshed out a bit more.