Allow including 'all' in a file (like git add -p)

[pimterry]

Currently you can only y/n each confirmation. If you've got a really big file though, which repeatedly matches, you might have to confirm quite a few times. If you have committed generated code in a repo, it's very easy to get false positives from this, and it'd be useful to have 'a' (for 'all') as an option, which confirms everything in the current file.