* Also accept lists and tuples as value of `depends_on`.
* The elements of the lists/tuples may be either Jobs or Job IDs.
* A single Job / Job ID is still accepted as well.
* Represent _all_ job dependencies in `Job.to_dict()`.
We now represent the entire list, instead of just the first element.
* Fix some doctext regarding plurality of dependencies.
* Add unit tests for job dependencies.
* One unit test establishes a pattern for checking execution order as affected by dependencies.
* Another unit test applies this pattern to the new capability to name multiple dependencies.
* Add unit test for new `depends_on` input formats.
Also test that these are properly persisted.
* Repair `Job.restore()`.
Need to convert bytes back to strings when reloading `dependency_ids`.
* Maintain backwards compat. in `Job.to_dict()`.
Keep the old `dependency_id` (singular) key.
* Provide coverage for new test fixture.
* Simplify some code.
Cut some superfluous `as_text()` calls left over from an earlier commit.
* Check for `dependency_id` in `Job.restore()` for backwd. compat.
Also eliminate use of `as_text()` here, in favor of `.decode()`.
* Switch to snake case instead of camel case.
* Eliminate some usages of `as_text()`.
Also cut some `print` statements.
* Cleanup.
* Accept arbitrary iterables for `Job`'s `depends_on` kwarg.
Instead of requiring a list or tuple, we now make use of `ensure_list()`.
* Add test fixtures.
* Provide a system to get two workers working simultaneously, using `multiprocessing`.
* Define a simple job that just says whether its dependencies are met.
* In `rpush`, make an option to record the name of the worker.
* Improve unit tests on execution order with dependencies.
These now actually have two workers going, which makes a more thorough test.
* Add unit test examining `Job.dependencies_are_met()` at execution time.
* Redesign dependency execution order unit tests.
* Simplify assertions.
* Improve doctext and formatting.
* Move fixture tests to new, dedicated module `test_fixtures.py`.
* Use `enqueue` instead of `enqueue_call` in new unit tests.
Hugo