Introducing: ActiveJob, and support for other queue adapters

• This removes the gem's direct dependency on delayed_job, in favor of an indirect dependency via activejob. As such, other DB-backed queue adapters can theoretically be supported!
• As a safety measure, the gem will now check in production that the queue adapter is :delayed_job, :que, :good_job, or :delayed. If it isn't in that list, the application will fail to boot. (Other adapters are allowed in non-production environments, and this gem now uses the :test adapter for its own tests.)
• The new job class is called Journaled::DeliveryJob. The DelayedJob-friendly equivalent (Journaled::Delivery) is still around for backwards-compatibility with any in-flight jobs. This will be removed in 4.0.
• This also trims down this gem's overall dependencies. Rather than depending on rails, it depends on railties, activejob, and activerecord. (And in its tests, it no longer depends on pg but instead uses an in-memory sqlite database.)

Add support for configuring HTTP timeouts

Summary
Current http_open_timeout is set to 15 seconds, which is causing some issues with today's AWS Kinesis outage. Make this value and some other timeout values configurable

Other Information
Journaled.http_idle_timeout (default: 1 second)
The number of seconds a persistent connection is allowed to sit idle before it should no longer be used.

Journaled.http_open_timeout (default: 15 seconds)
The number of seconds before the :http_handler should timeout while trying to open a new HTTP session.

Journaled.http_read_timeout (default: 60 seconds)
The number of seconds before the :http_handler should timeout while waiting for a HTTP response.

v2.3.1

This release contains no public-facing API changes, but instead of depending on aws-sdk-resources, the gem now depends on aws-sdk-kinesis, resulting in a significantly smaller dependency footprint.