Refactor harvesting scripts

[jacobthill]

There are some variant uses of OAI-PMH, etc. that pose problems for refactoring which include. These problems will need to be addressed when refactoring:

• [x] Harvest (or inversely, blacklist) specific sets by a command line flag
• [ ] Harvest part of a set. (e.g. two sets from AUC are partially approved)
• [x] Deal with cases in which sets are not used (e.g. QNL does not use sets. They have ~32k records and we only want the ~15k from the BL. These are indicated by the values of the physicalLocation element only, as far as I can tell.
• [x] Pass the metadataPrefix in a command line flag
• [x] Break xml doc into one record per file (this includes recognizes the record delimiter in various file structures)
• [x] Write records to collection/data/*.xml
• [x] Skip deleted records
• [x] move common methods to a separate module/file (e.g. to_str) and include where needed

Some of these should be pretty straight forward, others seem like they will require customization.

[jacobthill]

The partial set problem needs to be handled by harvesting and writing a separate script to delete records that we cannot keep. There are two many variables/unknowns to handle this at harvest time.