Fix alignment in Nat induction principle display.
Merge pull request #304 from mstone/master

Fix alignment in the Nat induction principle display. Thanks!
Fix spacing, close #306.
Fix spacing on page 50.
Typos in coproduct section.
Merge pull request #310 from derekelkins/master

Typos in coproduct section.
Merge branch 'master' of https://github.com/HoTT/book
Add missing close parenthesis.

Fixes issue 312.
Merge branch 'issue312' of github:rpglover64/book
Merge pull request #312 from rpglover64/issue312

Missing parenthesis in Ch. 1 exercises (p. 54)
Merge pull request #308 from rpglover64/master

Fix spacing on page 50, section 1.12.2
fixing typo in preliminaries
fixing typo in preliminaries
the paradoxes of self-reference are not specific to set theory
a remark about alternative universe handling
Merge pull request #316 from mikeshulman/selfreference

the paradoxes of self-reference are not specific to set theory
remove "merely" and mention "directedness" #317
clarify and index Fin(n), fix #294 and see #297
another example of a polymorphic function, close #297
fix #305