Improve tb-dev range-diff and diff-diff

Some improvements I want:

1. The command line auto-complete should also suggest tags.
2. tb-dev branch-range-diff and tb-dev branch-diff-diff should be renamed since it works with tags as well as branches.
3. tb-dev branch-range-diff and tb-dev branch-diff-diff should accept additional arguments to be passed to the underlying range-diff command.
4. tb-dev branch-diff-diff should filter out more context so that there are less false positives.
5. tb-dev branch-diff-diff should limit the output lines since meld has a character limit per line.
6. tb-dev branch-diff-diff should have an option to leave the git index and context lines unchanged. Useful if you are using meld with your own text filters.