This was anomalous, in that it contains &'static str, rather than a
proper nested error (eg a config::ConfigError, maybe).

But in fact it tursn out it is now not constructed.  The last
construction site was removed a long time ago in
  Use derive_builder for Authority and FallbackDir.

arti-config: Move cmdline to tor-config

See merge request tpo/core/arti!498

Improvements prompted by clippy, and disable one lint

See merge request tpo/core/arti!497

Provide and use macro for impl Derive via Builder

See merge request tpo/core/arti!499

Add correct serde(default) attrs for humantime_serde::option

See merge request tpo/core/arti!502

Discovered by a test case in my local tree.  The test case was
macro-generated by an extension of impl_standard_builder (which
macro istself currently awaiting review, arti!499)

Have also sent an MR to update the upstream docs
  https://github.com/jean-airoldie/humantime-serde/pull/8

The type of ret.map_err(codec_err_to_chan)? is ().  ISTM that
writing `let () = ` makes it clear that there is nothing there,
but the lint forbids this.

This lint is warn by default and trips here for me on current nightly.

It seems wrong to me.  We should be able to make it clear to the
reader that there is nothing here - note how this differs from the
lines below where Ready contains msg.  A let () binding is a good way
to do that.

I think the lint allow ought to be added everywhere, but that doesn't
seem easy right now - see this issue about maint/add_warning:
   tpo/core/arti#469

This does involve unwrap, but of course that can't fail unless the
formats fail, which would already panic (that's implied by format!).

This does not know anything about arti, only about TOML and Config.

Code motion, plus necessary import adjustments.

Tidy up ConfigurationSource a bit

See merge request tpo/core/arti!495

This will let other embedders use it.

These generic arguments weren't consistent.  It doesn't make sense ot
insist on getting a borrowed type and then cloning it.  So tidy things
up in the direction of taking owned values, which is what
ConfigurationSources actually needs.

(My personal preference would be &dyn to avoid monomorphisation code
bloat but that was controversial last time I proposed it somewhere.)

Discarding this error is not right.

It is not clear to me how this `pub enum` survived the "inaccessible
pub" lint.

This emphasises its nature.  We're going to provide a more cooked
constructor in a moment.

Improve documentation around Cargo features; make Runtime require Debug

Closes #445

See merge request tpo/core/arti!496

- #445 highlighted the lack of good documentation around Arti's
  multiple runtime support, as well as it being difficult to determine
  what runtime was actually in use.
- Improve the documentation to solve the first problem.
- To solve the second problem, make Runtime require Debug (which is
  arguably a good idea anyway, since it makes them easier to embed in
  things), and print out the current runtime's Debug information when
  arti is invoked with `--version`.
- (It also prints out other Cargo features, too!)

fixes #445

Refactor the tor-dirmgr bootstrapping code more gracefully

See merge request tpo/core/arti!488

Disable fs-mistrust in coverage CI.

See merge request tpo/core/arti!493

Remove cargo-husky, and replace with manual instructions

See merge request tpo/core/arti!494

A build script reaching into your .git/hooks/ and modifying them
nonconsensually was a bit of a horrifying concept, and also made it hard
to build arti with the feature disabled. Remove this crate, and replace
it with manual instructions on how to install the hooks in
CONTRIBUTING.md.

- Some FIXMEs got removed or amended.
- AddMicrodescs now yields a mutable reference, so we can use .drain()
  and reuse the allocation.
- Some panics were downgraded to debug_asserts.

- We don't want to inadvertently replace our netdir with one that's
  actually older, so detect and error on this condition.
- Also, print a debug line when we get a new netdir without enough
  guards.
- (An unrelated TODO was also added.)

- Taking a previous netdir directly and keeping it around before we need
  it is a bit of a waste of memory, and also doesn't mesh well with how
  SharedMutArc works.
- To remedy this, introduce a new trait `PreviousNetDir` and have the
  state machines take that instead. (I was a bit tempted to just pass in
  the SharedMutArc directly. Maybe I should've done that.)

The CI runners like to run as root with umask 000, which our code
rightly freaks out about.

- (Also fixes up some dirfilter stuff, whoops.)

- The only purpose of WriteNetDir was to provide a filter, which isn't
  necessary any more. Refactor to provide the filter directly.

- GetMicrodescsState now uses the NetDirChange API to propagate netdir
  changes, instead of modifying the netdir directly.
- PendingNetDir was refactored in order to support this use case.
- As a result, the netdir-related methods in WriteNetDir can be removed,
  leaving only the DirFilter for now.
- add_from_cache() no longer takes a store, because nothing uses it.
- (bodge: apply_netdir_changes() was put in a few places missed
  previously)

- The new DirState::get_netdir_change() API lets the state machine
  export a NetDirChange: a request to either replace the current netdir,
  or add microdescs to it.
- bootstrap.rs now consumes this new API, even though nothing implements
  it yet.
- This will let us implement GetMicrodescsState without having to
  directly mutate the netdir. The calling code also handles checking the
  netdir against the circmgr for sufficiency, and updating the consensus
  metadata in the store, meaning the revised GetMicrodescsState will not
  have to perform these tasks.

- The additional parameters passed to GetConsensusState are now passed
  through all the states, and used as well.
- WriteNetDir doesn't have a now() or config() method any more, since
  the states now get this from the runtime or the config parameters.
- This required modifying the tests to make a mocked runtime and custom
  config directly, instead of using DirRcv for this purpose.
- Additionally, because we don't have to upgrade a weak reference for
  DirState::dl_config(), that function no longer wraps its return value
  in Result.
- (A bunch of the FIXMEs from the previous commit that introduced the
  additional parameters have now been rectified as a result.)

Previously, CompoundRuntime would use the default implementations of
SleepProvider::now() and ::wallclock(), instead of using its wrapped
SleepProvider. This mildly embarrassing omission has been rectified.

- GetConsensusState::new now takes a set of parameters matching what it
  actually needs, instead of just taking a writedir. (It still *does*
  take a writedir, and indeed still uses it for basically everything,
  but that will eventually go away.)
- Its call sites were updated.
  - Some tests now need to take a runtime, and got indented a lot as a
    result.
  - Resetting was made non-functional, because we need to thread through
    the parameters passed to GetConsensusState to all of the other
    states, too. This will happen in a later commit.

- Given that this is effectively an implementation detail, it doesn't
  really make sense to have it be in the crate root...
- (also, we're going to change it a bunch now)

- fetch_single now takes what it needs, instead of an Arc<DirMgr<R>>.
- This required refactoring the CANNED_RESPONSE mechanism, given the
  test would otherwise fail due to not having a CircMgr to pass to
  fetch_single.