Add more options for commit filtering

[drdv]

Currently, only the -i and -n flags can be used to filter the commits to display. Consider adding support for some of the additional filtering mechanism discussed in man git-rev-list. In particular, the flag --since.

Supporting all the useful flags in git rev-list is not possible. Probably it would be better to have a flag that accepts directly a list of commits produced by git rev-list ....