In addition to " #pragma", " #error" should also be granted
an exception, since the unindented form would be rejected by
pre-ANSI C preprocessors.
  From Karl Heuer

Write documentation
  Include an example explaining how to use cppi as part of a cvs commit hook.

Add overwrite option -- maybe use GNU-style backup code.

Suggestion from Ulrich Drepper:
Add an option to convert code like this, removing unnecessary
parentheses and adding any spaces required to replace them:
  #if defined(FOO) || !defined (BAR)
to this:
  #if defined FOO || !defined BAR

Allow regex filtering (use Henry Spencer's new perl-like regexps)
   rather than hard-coding test for .c and .h suffixes

Add an option to enable the following (there's already support for it):
  Uli's suggestion for setting initial indentation level to e.g. -1
  for header files bracketed with #ifdef FOO_H/#define FOO_H...#endif.

Make sure we get a reasonable failure when cppi.l is modified
and flex is not available.

Likewise with cpp.gp and gperf (do this via the `missing' script).

Currently, the indentation width is hard-coded
at one space per nesting level.  Add an option to change that.

Add an option to tell cppi to ignore file-spanning directives like these:
#ifndef FOO_H
#define FOO_H
...
#endif FOO_H