Huey

* Big changes to simplify the way ``Huey`` is instantiated. No changes should
be necessary if already using ``RedisHuey``.
* Refactored the storage APIs and simplified the public interface. There is
now a single object, whereas before there were 4 components (queue, result
store, scheduler and event emitter).
* Added methods for retrieving and introspecting the pending task queue, the
schedule, results, and errors.
* Errors can now be stored, in addition to regular task results.
* Added metadata methods for tracking task execution, errors, task duration,
and more. These will be the building blocks for tools to provide some
insight into the inner-workings of your consumers and producers.
* Many new events are emitted by the consumer, and some have parameters. These
are documented [here](https://huey.readthedocs.io/en/latest/events.html).

What follows is a description of the changes between 0.4.9 and 1.0.0. There are
some backwards-incompatible changes to be aware of as well as new options for
the consumer. Most APIs are the same, however.


Backwards incompatible changes:

* ``huey.djhuey`` moved to ``huey.contrib.djhuey``. You will need to update
any import statements as well as your Django ``INSTALLED_APPS`` setting to
reflect the new module path.
* Redis backend is now the only one available, and the corresponding code moved
from ``huey.backends.redis_backend`` to ``huey.storage``.
* Removed the "RabbitMQ" and "SQLite" queue backends.
* Removed the ``-t`` and ``--threads`` option from the consumer. You should now
use ``-w`` or ``--workers``.
* Removed the ``-p`` and ``--periodic`` no-op options from the consumer. These
are enabled by default so the option had no meaning.
* The ``scheduler-interval`` option is configured using ``-s`` when previously
it was ``-S``. Furthermore, this must be a value between 1 and 60.
* Removed the ``peewee_helpers`` module.


New features:

* The queue consumer now supports multi-process or multi-greenlet execution
models (in addition to multi-threaded, which previously was the only option).
* Added `pending()`, `scheduled()` and `all_results()` methods to the `Huey`
class to allow introspection of the Queue's state at the current moment in
time.