Updated imports
Updated plugin exclusion implementation
Added checksum to StorageRecord. When processing items to store the checksum is use to determine if the latest version in the database is the same as the current item to be stored. If so, the item is skipped.
Added ExtractedDataItem class with attribute copying constructor.
Documented ExtractedDataItem and ExtractionPluginInterface classes.
Caused PostProcessedDataItem to extend ExtractedDataItem.
Updated signature of PostProcessingPluginInterface.process method.
Documented PostProcessDataItem and PostProcessingPluginInterface classes.
Updated signature of ValidationPluginInterface.validate method.
Documented ValidatedDataItem and ValidationPluginInterface classes.
Documented the FieldDefinition and DataModelPluginInterface classes
Updated Extraction CLI script to interface correctly with Post-Processing and Validation plugins.