Better do clang format

This is a smarter version of do-clang-format.py which does not rely on the find command and tries to minimize the number of files that are checked (since running clang-format is expensive).

usage: do-clang-format.py [-h] [--apply] [--all]

Run clang-format with the style file in the CORSIKA repository. By default it
finds new files and files with modifications with respect to the current
master and prints the filenames which need clang-formatting. Returns 1 if
there are files which need modifications and 0 otherwise, so it can be used
as a test.

optional arguments:
  -h, --help  show this help message and exit
  --apply     Apply clang-format to files which need changes.
  --all       Check all files below current path instead of new/modified.