Implement Sync for `IpcSender` (#415)

* Implement Sync for `IpcSender`

Our queue is a multi-producer queue, which by definition must
support concurrent sending.
Both crossbeam and the std::sync::mpsc queue (since Rust 1.72) implement Sync, hence
there is no reason not to implement this anymore.

Related zulip discussion: https://servo.zulipchat.com/#narrow/channel/263398-general/topic/Implement.20Sync.20for.20.60IpcSender.60/with/539930964

* fix unused_import

Publish 0.20.1. (#401)

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

Bump version to 0.20.0 (#390)

* Bump version to 0.20.0

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Revert rand back to 0.8

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Revert rand version change

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

---------

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

Mark `Router::add_route` as deprecated (#367)

* Propagate ipc errors to users of TypedRouterHandle

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Deprecate Router::add_route

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Bump Cargo.toml version

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Use semver-compliant version.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

---------

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>
Signed-off-by: Josh Matthews <josh@joshmatthews.net>
Co-authored-by: Josh Matthews <josh@joshmatthews.net>

Publish 0.18.3. (#360)

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

Release version 0.18.2 (#342)

I previously tried to upgrade the version, but since I was using an old
checkout my change was simply eliminated from the commit during merge.
This PR actually cuts a new version (0.18.2).

Support empty IpcSharedMemory (#335)

* Add tests for empty shared mem

* Simple empty slice

* Bump version to 0.18.1

Update to version 0.18 (#329)

This includes the new version of mio.

Use docs.rs for documentation link (#322)

Publish 0.16.0.