- Split the gigantic <tao.h> header in smaller headers.
- Make most structures opaque. Structure definitions are in
  <tao-*-private.h> headers.
- Reduce the number of rebuilt files when a header is modified.
- In code, TAO headers should be included first, then "config.h" (if
  needed), finally standard C headers.
- Eliminate compatibility code for Booleans (trust <stdbool.h>).
- If one is lazy, <tao.h> can be included; but it is generally
  sufficient to include a subset of the TAO headers.