Add astyle function to the supplied pre-commit hook script

It's a bit annoying (at least to me) when the head revision is not astyled properly.
When before commiting you call `run_astyle.bat` it results in getting diffs in seemingly random files (this hook fixes it), or the staged files getting seemingly random diffs (this hook should diminish such occurrences).
Should be pretty useful to both the people with commit rights and random contributors.
It supercedes `checkyear.sh`.

By the way, maybe it's better to rename `contrib` folder to `tools` or something? The current name is quite misleading.