Updated the endpoint for DPL data.
Updated importer column headers and related fixture files to reflect changes made to the source file.
Oversight in '#parse_american_date' describe title
Recreate CSL indices before importer specs run.
String#typeize now returns a symbol.
Makes model_class an instance method of Importer.
Importer#import_then_purge_old.
Add purge_old to CSL;

Also: add spec examples that test whether or not an importer can purge
old documents.
Adds can-purge-old-documents to Parature FAQ.
Add delay to mocked importer.

It seems that in some runs the importer purges olds docs before ES
assigns a timestamp to the new doc (just a guess). Anyway, this sleep
somewhat mimics real life usage so I'm ok with it.