Add CSS formating for deprecated parameters / methods
These aren't especially noticeable in the HTML docs.

![screen shot 2018-03-14 at 1 13 58 pm](https://user-images.githubusercontent.com/1312546/37422695-c9165cc4-2789-11e8-9939-7b3626f066ab.png)

Adding this to our CSS should fix that

```
div.deprecated {
    background-color: #ffe4e4;
    border: 1px solid #f66;
}
```

cc @datapythonista @shoyer 