Ayeaye

Added
- AbstractManifestMapper, EngineFromManifest to public interface

Added
- AbstractManifestMapper more flexible at supporting methods in subclasses by making manifest data available without specifying a fieldname or needing to access via an iterable.

Fixed
- unitests are skipped when modules aren't available

Added
- CsvConnector - added optional arguments: required_fields, expected_fields, alias_fields

Added
- PartitionedModel - starter for models splitting the work into subtasks

Fixed
- updated layout to better fit an easy life with packaging and distribution.

Fixed
- Moved from build-0.4.0 to build-0.5.1 as sub packages were appearing at top level
- removed lazy methods in AbstractManifestMapper. They are too complicated to get right when the subclass is used as a class variable that depends on another descriptor.

Added
- AbstractManifestMapper is now a descriptor

Changed
- AbstractManifestMapper iterator uses single engine_url instead of list of 1 item. Hopefully this is more intuative.