The other files were already indirectly referenced, but it's good to
make it explicit.

Because, even in 2022, there are systems where the libc locale is not,
in fact, UTF-8. Fixes #186.

Change "eigth-block" to "eighth-block"

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.

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.

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.

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.

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.

This complicated the scan code more than I had anticipated and has a
few inherent bugs with respect to calculating shared hardlink sizes.

Still, the merge approach avoids creating a full copy of the subtree, so
that's another memory usage related win compared to the C version.
On the other hand, it does leak memory if nodes can't be reused.

Not quite as well tested as I should have, so I'm sure there's bugs.

In a similar way to the C version of ncdu: by wrapping malloc(). It's
simpler to handle allocation failures at the source to allow for easy
retries, pushing the retries up the stack will complicate code somewhat
more. Likewise, this is a best-effort approach to handling OOM,
allocation failures in ncurses aren't handled and display glitches may
occur when we get an OOM inside a drawing function.

This is a somewhat un-Zig-like way of handling errors and adds
scary-looking 'catch unreachable's all over the code, but that's okay.

Performance is looking great, but the code is rather ugly and
potentially buggy. Also doesn't handle hard links without an "nlink"
field yet.

Error handling of the import code is different from what I've been doing
until now. That's intentional, I'll change error handling of other
pieces to call ui.die() directly rather than propagating error enums.
The approach is less testable but conceptually simpler, it's perfectly
fine for a tiny application like ncdu.

I plan to add more display options, but ran out of keys to bind.
Probably going for a quick-select menu thingy so that we can keep the
old key bindings for people accustomed to it.

The graph width algorithm is slightly different, but I think this one's
a minor improvement.

The exported file format is fully compatible with ncdu 1.x, but has a
few minor differences. I've backported these changes in
ca51d4ed