Tell `\cref` how to typeset references to the appendix.
Stylistic changes to appendix, removing unecessary scary type-theoretic lingo.

These changes also pertain to #143, #125 and #128.

* removed all those future tenses
* rephrased where I thought the type theory jargon was overdoing it
Merge branch 'master' of github.com:HoTT/book

Conflicts:
	formal.tex