Fix ind(D,d,x,y,p) in (i), (ii) and (iii) of Lemma 2.1.4

ind(D,d) : \Pi_{x,y : A} \Pi_{p : x = y} D(x,y,p) according to
Section 1.12.1 (Path induction).
Add some style
Merge pull request #696 from kirelagin/patch-2

Add some style
Correction in proof of Thm 4.9.4
Errata for 2c194835, unmarked
Merge pull request #697 from TimRichter/proof494

Proof494
first-order fix to the induction principle of V
unmarked errata for 6d9722d
correct merge marker so Travis can update it
Mark Errata (auto)
Merge pull request #693 from ahorn/lemma-2.1.4

Fix ind(D,d,x,y,p) in (i), (ii) and (iii) of Lemma 2.1.4
Merge pull request #698 from mikeshulman/Vind

first-order fix to the induction principle of V
Mark Errata (auto)