Use clang-format to normalize the coding style

Browsing through the volumeicon code here on github makes it fairly obvious that there is no consistent coding style used throughout the codebase. (I'm certainly guilty of adding to this problem myself.) I therefore propose to use an automatic formatting tool like clang-format to keep things a tad more coherent from now on. Obviously, coding style is always a controversial issue, but I think most people would agree that consistency is desirable even if they disagree on specifics like brace style, indentation, etc.

These commits add a sample configuration file for clang-format, as well as a script to format all files under src/ in place. Consider this PR a suggestion rather than something I want to land as is.