Provide .clang-format or update astyle

[daniel-j-h]

It seems like this project is not using a .clang-format style file for formatting. Using make indent (which calls astyle with some options) wants to re-format basically the whole source tree for me.

@joto what's your take on this? Also what do you think about documenting this in the dev docs?

[joto]

Years ago I used astyle, but haven't used it in a long time. So it is a sort-of left-over from before as you can see by the fact that it is defined in the Makefile and not in the CMake config. Astyle seems to be unmaintained and doesn't work well with modern C++, so that is a dead end there. I wanted to switch to clang-format, but getting it to do what I want isn't that easy if at all possible. Only rather new versions are usable at all. So for the time being I am stuck with manual formatting. Now that more and more other people are contributing code, this should probably be "fixed".

TODO items:

• Find suitable clang-format definition
• Remove astyle stuff.

[joto]

Astyle stuff has been removed in 76e153d.

I experimented with clang-format-3.8 but aren't very happy. It is rather buggy and doesn't support common formatting choices like indented nested preprocessor directives.