This is where the FallbackList type is.  We are going to want to
provide a builder too, which ought to impl Default.

This means that the default value for the type must be next to the
type.  In any case, it was anomalous that it wasn't.

This commit is pure code motion.

This commitid is the current head of my MR branch
  https://github.com/colin-kiegel/rust-derive-builder/pull/253
  https://github.com/ijackson/rust-derive-builder/tree/field-builder
Using the commitid prevents surprises if that branch is updated.

We will require this newer version of derive_builder.  The version
will need to be bumped again later, assuming the upstream MR is merged
and upstream do a release containing the needed changes.

We will need the new version of not only `derive_builder_core` (the
main macro implementation) but also`derive_builder` for a new error
type.

This patch removes files created by older versions of arti, if they
are at least 4 weeks old.

Closes #282

Instead of just having a function that recalculates the latest clock
skew, instead recalculate the clock skew when it may have changed,
and notify other processes via a postage::watch.

This time, our estimator discards outliers, takes the mean of what's
left, and uses the standard deviation to try to figure out how
seriously to take our report of skew/not-skew.

These estimates are still not actually used.

(This is just a placeholder; I'm going to make the functions
smarter in the next commit.)

Upstream 0.8.2 has broken compilation with Rust 1.53; versions
0.8.{0,1} have been yanked.

Possibly by the time the next arti version comes out, they'll have
fixed this situation, or we'll have upgraded our MSRV.

Upstream issue at https://github.com/Nugine/rlimit/issues/42 .

Also add tests for RetryTime comparison functions to make sure they
work as expected.

This is necessary to fix build for M1 apples.

Not all of these strictly need to be bumped to 0.2.0; many could go
to 0.1.1 instead.  But since everything at the tor-rtcompat and
higher layers has had breaking API changes, it seems not so useful
to distinguish.  (It seems unlikely that anybody at this stage is
depending on e.g. tor-protover but not arti-client.)

Unlike the rest of the crates, these don't have a "tor-" or "arti-"
prefix, and are potentially used by code outside arti.  With that in
mind, it's probably for the best not to bump them to 0.2.0 along
with the rest of our crates.

They have had no changes since 0.1.0 other than refactoring and
changing of clippy lints.  Therefore, I'm not bumping the
dependencies from other crates onto these: it's fine whether our
other crates use caret/retry-error 0.1.0 or 0.1.1.

This feature allows us to detect different failing cases for
arti#329 that would otherwise be hard to induce.  It works by
filtering consensus directory objects and/or microdescriptor objects
before introducing them to the directory manager.

Closes #397.

This commit uses the `visibility` and `visible` crates to
conditionally make certain structs and their fields public
(respectively).  This is incredibly dangerous to use for anything
besides testing, and I've tried to write the documentation for the
feature accordingly.

The guard manager is responsible for handing out the first hops of
tor circuits, keeping track of their successes and failures, and
remembering their states.  Given that, it makes sense to store this
information here.  It is not yet used; I'll be fixing that in
upcoming commits.

Arguably, this information no longer belongs in the directory
manager: I've added a todo about moving it.

This commit will break compilation on its own in a couple of places;
subsequent commits will fix it up.

This is the logical place for it, I think: the GuardMgr's job is to
pick the first hop for a circuit depending on remembered status for
possible first hops.  Making this change will let us streamline the
code that interacts with these objects.

The various background daemon tasks that `arti-client` used to spawn are
now handled inside their respective crates instead, with functions
provided to spawn them that return `TaskHandle`s.

This required introducing a new trait, `NetDirProvider`, which steals
some functionality from the `DirProvider` trait to enable `tor-circmgr`
to depend on it (`tor-circmgr` is a dependency of `tor-dirmgr`, so it
can't depend on `DirProvider` directly).

While we're at it, we also make some of the tasks wait for events from
the `NetDirProvider` instead of sleeping, slightly increasing
efficiency.

(Doing this a few days ahead of time to give updated code time to
get testing)

Code motion and import fixups.

Code motion and import fixups.

Now we use NetParams.  That implies making its constructor public,
which I think it fine.

This is related to #413 but is far from completing that ticket.

this also removes JoinResult

This has the different syntax for builder field attributes than what I
originally proposed in my MR, and which therefore is in the pinned
branch.

My upstream MR for the field attributes feature was morged:
  https://github.com/colin-kiegel/rust-derive-builder/issues/239

This (almost) a pure code-movement commit: it also makes one public
function private in order to suppress a warning.

We have upstreamed this code.

This reverts commit 6193c9d9.

This has the humantime_serde::option module, which we have upstreamed
and are about to switch to.

The remaining dependency with  version = "1"  is going to be removed
in a moment.

This enum was otiose: its set of valid values is precisely those of a
Vec.  (Indeed what would TokVal::Multi(vec![]) have meant?)

We are going to want to specify custom attributes on fields of the
builder struct.  This feature was missing from derive_builder.

This commitid is the current head of my MR branch
  https://github.com/colin-kiegel/rust-derive-builder/pull/237
  https://github.com/ijackson/rust-derive-builder/tree/builder-field-attrs
Using the commitid prevents surprises if that branch is updated.

We will require this newer version of derive_builder.  The version
will need to be bumped again later, assuming the upstream MR is merged
and upstream do a release containing the needed changes.

This commit adds support for a BrokenTcp provider that can make
connection attempts fail or time out.  It doesn't yet have a way to
turn on the failure.

This will be used to allow our config *builder* structs to be
Deserialize.

Code motion and the minimal mechanical changes.

As per
  tpo/core/arti!375 (comment 2783078)