Ayeaye

Added
- a custom exception for when a subtask fails
- optional PartitionedModel.partition_subtask_failed hook to allow models to handle subtask exceptions

Changed
- default behaviour on subtask fail in a PartitionedModel to raise the SubTaskFailed exception
- LocalProcessPool to cleanup orphan Processes on deconstruction
- TaskFailed to include a couple of extra fields - model_class_name and resolver_context

Fixed
- serialised task messages were being yielded by `LocalProcessPool`

Added
- richer classes (ayeaye.runtime.task_message) for task message within processing pool

Changed
- yield type from `AbstractProcessPool.run_subtasks`

Removed
- ayeaye.runtime.multiprocess.MessageType

Added
- AbstractProcessPool to make it easier to add custom process pools - see the Fossa project

Changed
- PartitionedModel to have injectable :class:`AbstractProcessPool`
- ProcessPool - moved arguments from constructor to run_tasks to make it easier to customise subclasses of ProcessPool
- renamed: ProcessPool to LocalProcessPool to clarify the difference with the new pool being created in the Fossa project

Removed
- model_initialise option in ProcessPool as ProcessPool is only used by PartitionedModel which doesn't use it and it's simplier without.

Added
- common pattern to make it easy to add datasets to a MultiConnector
- `method_overlay` argument to Connector to allow explicit naming of the new method which makes it
cleaner and more intuative with callables (instead of plain functions)

Added
- Two optional args to CsvConnector. 'quoting' - to pass a mode through to the CSV module and 'transform_map' so a callable can be used at the field level. This is a useful mechanism to make small field level adjustments (e.g. tranforming types) during IO.

Fixed
- RestfulConnector using wrong fieldname within an exception