evancz/Elm — pull request #469 by ibizaman (2014-01-21 20:11:32+00:00)
Title: use dict headers for http request and response

Following [this discussion](https://groups.google.com/forum/#!topic/elm-discuss/9AOFt2j72H8), I added headers handling on the Response side of the Http library.

Furthermore, I used a dictionary instead of list of tuples for the headers. I think this is more suited for what one would one to do with headers: search for the value associate with a header.