tweak intro to ch 8
MSC2010 classification, close #257
Better back references in bibliography, cf. #254

Feel free to remove the parentheses. The main advantage over the
old version is that it correctly detected singular vs. plural.
Rename linear order to weak linear order, close #237
Arabic page numbers in front matter, close #256
Correct frontmatter pagination, close #256 again
Revert "Correct frontmatter pagination, close #256 again"

This reverts commit f8d9722e7bdc93d94fe288d3a968629af1d82917.
wording/formatting in ch 8
Merge branch 'master' of github.com:HoTT/book
typo
wording/formatting in ch 9
Revert "Revert "Correct frontmatter pagination, close #256 again""

This reverts commit 9e6d54c2b90cf16a12e413fbd14388cced9a8abb.

I am trying to fix some internal bug that github reported to me.
Merge branch 'master' of github.com:HoTT/book
wording/formatting in ch 10
Fix well-founded induction.

On re-reading, I couldn't make any sense of the proof of 10.3.2.  In
order to fix it, I found I needed to write out the induction principle
for accessibility more carefully, which is probably a good idea anyway.
Fix proof of union axiom for V

I don't think f\circ\pi was the right map.
Merge branch 'master' of github.com:HoTT/book
wording/notation in Ch 11
use \Parens, \blank, \widehat where appropriate
formatting of some equations