[Feature request] "Hooks" for git log

Hello,

While it's possible to filter commits in `git log` by their contents with --grep and -S options, it's not always possible for formulate desirable filter in their terms.

I think it would be very useful if git log provided new option named e.g. --hook or --script, which would take script path as an argument. git log would follow it's normal way of operation, applying other filtering options it was given, however intstead of printing info on commit that matches filters, it invokes script with commit hash as an argument. Script can do whatever it needs with hash, including any git operations, can print commit info to log if needed, or print something else, or keep silence. If script returns non-zero, parent git log command terminates, otherwise it continues.