Linkerd 1.4.0 upgrades us to the latest versions of Finagle and Netty and
features lower memory usage for large payloads. Two new configuration options
have been introduced: client connection lifetimes and access log rotation
policy. One breaking change has been introduced around the configuration file
syntax for loggers.  This release features contributions from ThreeComma,
[ScalaConsultants](https://github.com/ScalaConsultants), [Salesforce](https://github.com/salesforce), and [Buoyant](https://github.com/buoyantio).

* **Breaking Change**: Rename the loggers section of the Linkerd config to requestAuthorizers to match the name of the plugin type ([#1900](https://github.com/linkerd/linkerd/pull/1900))
* Tune Netty/Finagle settings to reduce direct memory usage ([#1889](https://github.com/linkerd/linkerd/pull/1889)). This should dramatically reduce direct memory usage when transferring large payloads.
* Introduce a ClientSession configuration section that provides ways to control client connection lifetime ([#1903](https://github.com/linkerd/linkerd/pull/1903)).
* Expose rotation policy configuration for http and http2 access logs ([#1893](https://github.com/linkerd/linkerd/pull/1893)).
* Stop logging harmless reader discarded errors in k8s namer ([#1901](https://github.com/linkerd/linkerd/pull/1901)).
* Disable autoloading of the default tracer in Namerd ([#1902](https://github.com/linkerd/linkerd/pull/1902)). This prevents Namerd from attempting to connect to a Zipkin collector that doesn't exist.
* Upgrade to Finagle 18.4.0.

Signed-off-by: Alex Leong <alex@buoyant.io>