Moved book generation code into PDF directory

Start of a reorganization of files to make book more browable and to
reduce the size of links to chapters.

pdf/short_build_book

@@ -0,0 +1,11 @@
+#! /bin/bash
+
+echo "merging book..."
+
+python short_merge_book.py > short.ipynb
+
+echo "creating pdf..."
+ipython nbconvert --to latex --template book --post PDF short.ipynb
+
+echo "done."
+