adds SearchWorksMarc and Instrumentation support

Fixes #268 

Adds `SearchWorksMarc` class with subclass `Instrumentation`. For customization based off various marc fields, base private methods in `SearchWorksMarc` can be overridden by a subclass.

### Fixture 43
![screen shot 2014-08-11 at 11 43 53 am](https://cloud.githubusercontent.com/assets/1656824/3880793/8d5642a0-2187-11e4-9dd8-f1979dc4b2c9.png)

### 10246987 
Note there are some issues with this record's metadata, which is why things like "doubling 1" appear. Has been reported to metadata team.
![screen shot 2014-08-11 at 11 45 57 am](https://cloud.githubusercontent.com/assets/1656824/3880809/c7e16d00-2187-11e4-9da6-a489513b47ab.png)


Can we memoize this under `@marc_instrumentation` instead of under `@marc_382`?  Not likely to cause any problems down the road but that way we don't get tripped up anywhere else if we were to try and use that ivar somewhere else in the SolrDocument class.  If it's named the same thing as the method it would be easy to track down why.