Merge pull request #22 from sebhoss/cleanup

Some minor code cleanups
Replace ${file_name} with the current file name.

Fixes #1 by passing Document#file.getName() to the header. The header
then replaces every occurence of $[file_name} with the given file name.
This is a workaround for the fact that the header is otherwise
constructed before a certain file is opened.

Signed-off-by: Sebastian Hoß <mail@shoss.de>