Add notes for first lecture
Partial cleanup of main text

No content is changed in this commit; it just replaces some of
the description lists in the intro text to a defninition
environment.
Remove R lecture file -- same code is in md
Edits to ARMA material
Tweak acronyms in preamble
Merge 'intro' branch

This branch moves the introductory ARMA modeling material into the
main part of the text"
Bump version to 0.2.2