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)


Will `@marc_record.group_by(&:tag)` work here?