add .org file for notes

Separating the notes into an .org file is just more sane than what I
was doing, which was putting my notes into prolog comments. Now the
prolog files will primarily contain just Prolog code, with some light
commentary and my notes will be far easier to read.

learn_prolog_now.pl: remove chapter 1 notes.
learn_prolog_now.org: add chapter 1 notes.
transfer all notes, add ch. 4 notes

learn_prolog_now.org: Move chapter 2 and chapter 3 notes into .org file