Macvim

I changed the line number/gutter background colour to match the style from the screenshots.

The background colour for Pmenu was the same colour as the normal background colour, which was difficult to make out. I changed the background colour to the foreground, and selected a lighter colour from the theme as the foreground.

I added a generic Parameter definition since the only other ones I saw were rubyBlockParameter and cssURL. This way, people will be able to set the HiLink colour to Parameter in their vim syntax files.

Before
![before](https://cloud.githubusercontent.com/assets/828125/4469985/98b2ac76-491c-11e4-9e1a-6e8c0b396d1f.png)

After
![after](https://cloud.githubusercontent.com/assets/828125/4470008/134b573a-491d-11e4-9c47-cc1e717e868d.png)