Tweaks to interpretations changes parsing

Highlights:

1. Allow "under" to indicate that we're in an interpretation context. "Under 2(b)", for example.
2. Turn AMDPAR text into plain text rather than carrying around tags
3. Add the ability to replace an xml node with plain text that contains inserted spaces (to account for missing spaces in FR's XML)
4. Allow the "Supplement I" indicator (when determining where to start parsing) to be in any case