Highlight operators in Haskell.

IMO, highlighting operators in Haskell improves readability a lot. I picked orange since it's easy to tell apart from the existing colors, even for small operators like `.`

![haskell-jellybeans](https://f.cloud.github.com/assets/20756/44783/96e3b7c4-56fb-11e2-8387-5ae67ab4ccdf.png)

I put it near the end of the list of language-specific highlights, but I can move it if you have a specific order. Thanks in advance!