Merge pull request #227 from khandelwal/supp

Allow parsing of 'introductory text of paragraph 1'
Catch 'heading of comment ...' the same way we catch 'heading of paragraph'
Merge pull request #228 from cmc333333/header-of-comment

Catch 'heading of comment ...'
Allow citations of a part + section + paragraph without the section marker
Merge pull request #229 from cmc333333/sxs-diff-reg

Catch another type of citation
Add spaces to appendices' text
Add spaces to table headers and cells
Unfold EXTRACT tags for SxS computation
Merge pull request #231 from cmc333333/sxs-extract

Unfold EXTRACT tags for SxS computation
Merge pull request #230 from cmc333333/appendix-spacing

Make sure spaces are added when appropriate in appendices