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)

No `map` will throw an error.  Could do something like

```
@subfields = options[:subfields]
  .map { |s| CustomMarc::Subfield::Instrumentation.new(s.code, s.value) } unless options[:subfields].nil?