As per #309

Update all references.  There is one remaining hit for
  git-grep '\.sh\b'
namely "build.sh" in maint/reproducible_build, which I think is
the build script for osxcross - ie, an external project.

Remove some needless refs and slicing

See merge request tpo/core/arti!327

These (&foo).into() constructions are needed so we use the
implemnetation of `From<&Foo>`, not a recursive call to this very
function.

This is a partial revert of the previous commit.  I'm making this a
separate commit for the benefit of posterity.

We can't use discriminants here now, but maybe we can in the future.

Make CircMap open_ent_count O(1)

See merge request tpo/core/arti!302

arti: create TorClient first, then bootstrap.

Closes #336

See merge request tpo/core/arti!320

Fix typos

See merge request tpo/core/arti!326

So we get a stack trace

We're about to reuse this and we'll want it to take the higher-level
type.  Also it seems more proper like this.

Prompted by nightly's clippy (which has some false positives, so is
currently disabled).

Re-enable clippy::ptr_arg where it had been disabled.

See merge request tpo/core/arti!323

Closes #322.

This isn't complete (see TODO), but it's enough to let us report the
right ErrorKind if something fails to parse.

It had too many possible Kinds depending on what kind of string had
failed to parse.

I decided to use #[source] here instead of #[from], so that we
would have to explicitly convert these errors where they show up.

At first I had thought that all sqlite errors would be internal, but that's
not the case.

arti-client: add ability to automatically bootstrap

Closes #278

See merge request tpo/core/arti!322