major enhancements (complete rewrite and new features):

- work on Windows (no more requirement of Unix "head")
- use IO::Open3 in place of ``: no shell is invoked anymore
- use custom log from git to limit output size and increase efficiency
- support for fixed-length keywords (ie. SVN $Author::     $)
- keep keyword case unchanged in both directions
- support for $Rev$ as well as for $Revision$