Issue title: Syntax highlighting bug
 Issue body: Hi, 

The type of function parameters is not correctly _highlighted_.

The bug: 
![screen shot 2013-07-24 at 01 08 59](https://f.cloud.github.com/assets/504977/845630/e5da6114-f3ec-11e2-80c3-deabbf6c0aec.png)

How it should look like:
![screen shot 2013-07-24 at 01 10 47](https://f.cloud.github.com/assets/504977/845645/290ca8de-f3ed-11e2-8865-6237b9550555.png)

I'll try to check it out later. 

 Comments: 
 Comment 0: It's the `typeScriptParameters` match that does that. The current way is overriding any other highlighting that recognised words like `string` and `number` would normally have. I'm not sure yet how to deal with it.

{'source': 'GithubIssues', 'repo_name_with_owner': 'leafgarland/typescript-vim', 'issue_id': 17131217, 'repo_stars': 1843.0}