Fix issue with diff url for individual paragraphs within chrome
Add intro interps to toc structure
SectionUrl points to the correct url for interp intros
Chrome-based paragraphs use the same template as sections; build the tree around the one paragraph in view
Intro interp header has title as sub_label so it looks like the rest of the TOC entries
PEP8
Merge pull request #554 from cmc333333/interp-intro

Display intros to interpretations