iterate id and zipWith/repeat rules (Closes #41)

[nomeata]

I was correcting a Haskell exam and found that some students would write
such code. Hopefully these students will use hlint when they do real
programming.

[ndmitchell]

Thanks, these hints look very nice.

[ndmitchell]

The hints were nice but there were a few syntactic wobbles - mostly using ==> instead of = and you can't use xs in a hint - it must be x (single letter variables are considered unbound). I've fixed those after. I'm planning to write QuickCheck tests for these things soon.

[nomeata]

sorry for not testing them, it looked simple enough™ :-)

[ndmitchell]

I took a quick look and spotted nothing wrong, but my travis instance did - I rarely test my code anymore, just let automated services do it for me!

[nomeata]

Hmm, shound’t travis have tested my pull request before you merged it?

[ndmitchell]

Yes, and last week it would have. But at the moment Travis is having a bit of a wobble (it was yesterday as well) so the tests show up after-the-fact, with little indication it might intend to do a test. I notice that now it has tested your patch and rejected it, but when I merged, it didn't even have the "in progress" symbol.