Standard C imposes that names prefixed by `_` and types suffixed by `_t`
are reserved).  Hence:

- Public symbols and macros are prefixed by `tao_` and `TAO_`.

- Private/helper symbols and macros are prefixed by `tao__` and `TAO__`.

- Types are no longer suffixed by `_t`.

- `struct`/`enum`/`union` have the same name as their `typedef`
  counterpart.

- Headers define a macro `TAO_..._H_` to avoid being included more than
  once.