Remove using std.
cosmetics: add new lines at the end of files.
Don't use camelcase words in About dialog anymore.
contrib/checkyear.sh: include pl files in the check.
Bump copyright year for modified files.

Everyone with push rights has to use the precommit hook.

(Hint: `cp contrib/checkyear.sh .git/hooks/pre-commit`)
Use `#pragma warning(push/pop)` instead of `#pragma warning(default)`.
Simplify preprocessor config.