apply clang-format to the source code

apply clang-format to the source code

The source and headers have been treated slightly differently.

The source files (*.c) have had clang-format applied and it's expected
that this will become an automatic process in the future.  A few blocks
of source have been protected from change by special comments
    // clang-format off
    // clang-format on

The header files contain a lot of #define'd lists which contain a lot of
manually placed whitespace.  clang-format doesn't have an option to
align these as we'd like.

The compromise was to run clang-format on the headers, but cherry-pick
the formatting that was more human-friendly.  clang-format won't be
automatically run on the headers.

This commit also sorts out a few other formatting issues:
- All tabs have been expanded
- Tabs in translated strings have been expanded
  (this makes it easier to align translated strings)