implement marc382 parsing

Fixes #268 

Sets up a pattern but not generic classes to add custom marc parsing outside of helpers.

## 10246987
![screen shot 2014-08-06 at 3 47 37 pm](https://cloud.githubusercontent.com/assets/1656824/3835242/d1cf5798-1dbb-11e4-915d-ddd1d0928184.png)

When `options[:subfield]` isn't supplied will `subfields_to_text` throw an error when calling `each_with_index` on the now nil instance variable?