Add vim Keyword syntax coloring to Tomorrow-Night-Eighties

Orange might not be the best choice, so I'm open to other suggestions,
but I think something is better than nothing.

Before change (on a Scala file):
![screenshot 2014-01-20 18 36 16 2](https://f.cloud.github.com/assets/977929/1959348/fa264b92-822b-11e3-9ef6-d96613f3a63c.png)

After change:
![screenshot 2014-01-20 18 35 52](https://f.cloud.github.com/assets/977929/1959352/0057934a-822c-11e3-9695-0d1f6ffcfed1.png)