Add last_answer to the Interactive mode

[cherichy]

I don't want to type Y or N everytime, so just push Enter for the last answer.

[jgonggrijp]

Thanks for your pull request! Would you mind adding two more things?

1. Show the default answer in the default prompt. For example by appending [y] if the previous answer was y and [n] if the previous answer was n.
2. Add a test to tests/review.t so that we can confirm that the feature still works in the future.

Thanks in advance!

[cherichy]

I have added the default answer, but I am not familiar with the syntax of the test file. So I did not change the test file. Sorry about that.

[jgonggrijp]

No problem, thanks for your work so far. I'll take it from here. If somebody else is faster, please go ahead.