Various typo and explanation fixes

Too many to mention. Read through several chapters and made changes
as I went. I've had people (correctly) question me on several points,
and pointing out typos.

pdf/readme.txt

@@ -0,0 +1,22 @@
+This directory contains code to convert the book into the PDF file. The normal
+build process is to cd into this directory, and run buil_book from the command
+line. If the build is successful (no errors printed), then run clean_book from
+the command line. clean_book is not run automatically because if there is an
+error you probably need to look at the intermediate output to debug the issue.
+
+I build the PDF my merging all of the notebooks into one huge one. I strip out
+the initial cells for the book formatting and table of contents, and do a few
+other things so it renders well in PDF.
+
+There is some code to do the same from Windows (.bat files), but they are now
+a bit out of date.
+
+There is also some experimental code to convert to html.
+
+The files with short in the name combine only a couple of notebooks together.
+I use this to test the production without having to wait the relatively long
+time required to produce the entire book. Mostly this is for testing the
+scripts.
+
+No one but me should need to run this stuff, but if you fork the project and
+want to generate a PDF, this is how you do it.