
Refactoring the book:

 - Move constructor-debugging.md to new section.  It has nothing
   to do with the constructor example.
 - Transforming names and strings goes into a new example,
   possibly about discriminants.
 - Discussion of "expect items" is out-of-place and unmotivated.
 - "Naming conventions" is not exactly an "advanced topic".

Unmentioned keywords and conditions from the reference:
 - $crate
 - $dbg_all_keywords
 - $error
 - $Xattrs
 - $ignore
 - $tdefkwd
 - $tdefgens
 - $tgnames
 - $vdefbody ?

 - approx_eq
 - dbg
 - fdefvis
 - is_empty
 - is_struct, is_enum, is_union
 - v_is_named, v_is_tuple, v_is_unit

Mentioned but unused in examples:
 - all, any
 - $fvis
 - vmeta
 - tgens
 - name and string manipulation

Concepts to explain:
 - Using the const _:()={...} trick.
 - Namespace management.
 - Using macro_rules!()
 - Generating rustdoc documentation for your generated things.
 - Debugging (more detail)
 - Examples to stress-test your template.
 - Fancy use of vpat to implement a cross-product style destructuring.
 - The complete syntax for expansions, conditions
 - The complete template syntax
 - Silly prelude tricks.
