Add an optional delimiter parameter to #mods_record_field.

Only implemented for language at the moment.

### ww121ss5000
#### Before
![ww121ss5000-before](https://cloud.githubusercontent.com/assets/96776/4170929/f8b98480-3537-11e4-9a25-670a50136de3.png)

#### After
![ww121ss5000-after](https://cloud.githubusercontent.com/assets/96776/4170928/f8af8ff2-3537-11e4-987e-50c80b9baf34.png)