Many improvements for usability and debugging

- bugfix in the git feeder: sometimes it showed commits even if not in the specified remote/branch
- now you don't have to be in the project directory, you can specify the target project on the command line
- new custom interval 0 means to exit after one run, useful for debugging
- new `--relstart` option to be able to start from HEAD - Nth revision -- instead of N = 10 hardcoded
- renamed feeder scripts to be more simple, for example `git.sh` instead `feeder-git.sh`, they are all in a `feeders` directory anyway
- the feeders are easier to debug: they print usage info when you run them without params
- changed the timestamp converter in the bzr and svn feeders to use perl instead of python -- more portable
- updated readme accordingly
- several bugfixes in the bzr and svn feeders