Rewrite theory for OOS statistics

This commit reorganizes and rewrites the OOS theory section; it puts
the lemmas before the main theorem and hopefully will be more clear.
It also moves the example after the full-sample section, and consolidates
the OOS-t and the variance estimator results.
Reorder proofs of main results in appendix
Edit proof of mixingale result
Fix typo in convergence lemma
Edit proof of Theorem 1
Minor edits to variance-related lemmas
Edit interval and testing proof
Tweak subsection heading for OOS results
Start ot edit introduction for in-sample material
More edits (at home)
Intermediate work on paper
intermediate
Working on examples
Intermediate commit
Start to fill in in-sample examples
Editing
Format and sort bibtex file
Change some italics macros to 'emph'
Small edits to introduction
Small edits to assumptions and setup