add a summary of the revisions

popl19/revisions.md

+We summarize the major changes to the paper. There are also some minor
+typo fixes/re-wordings in various sections.
+
+1. To clarify the applicability of the main results, we added a few
+   paragraphs to the discussion section at the end to discuss what
+   languages should be models of GTT, how things like reference
+   equality fit in and the difference between call-by-name and
+   Haskell's notion of laziness. We also put some forward references
+   to this discussion in the introduction.
+2. We expanded the related work a great deal, adding comparisons to
+   Henglein and Degen and Thiemann's work. We also clarified that AGT
+   is based on the *type safety proof* of the static language, and not
+   just its dynamic semantics.
+3. We added an explicit list of contributions to the end of the
+   introduction.
+4. The list of contributions has forward references giving an overview
+   of the paper structure, and we also added an overview to the
+   beginning of section 2.
+5. To avoid "story of discovery" with the dynamic type models, we
+   mention type tags and how this is the usual way of constructing a
+   dynamic type for the value type and the novel aspect is the fact
+   that the dual is useful for interpreting the dynamic computation
+   type.
+6. We named the rules, specifically in figures 1-5.
+7. We re-ordered some paragraphs in the introduction to introduce eta
+   equality before the discussion of eager and transient cast
+   semantics.