add js function defination syntax match

Hello,

I have added the _jsFuncDef_ syntax match for the function definition highlight. Because _sublime text_ highlight it that way and it is really easy to quickly grab the defined function 'name' with this highlight.

This is my work out via my [monokai](https://github.com/crusoexia/vim-monokai) color schema:
![screen shot 2014-11-29 at 12 21 12 am](https://cloud.githubusercontent.com/assets/5928754/5230297/16fbf7c0-775f-11e4-9436-4368e3350ceb.png)

Compare with sublime text 3's version:
![screen shot 2014-11-29 at 12 21 35 am](https://cloud.githubusercontent.com/assets/5928754/5230303/2dac373c-775f-11e4-9b9f-f7c01070be03.png)

And a real example:
![screen shot 2014-11-29 at 12 20 12 am](https://cloud.githubusercontent.com/assets/5928754/5230305/3d0d2c7c-775f-11e4-8747-fbc78e08f375.png)

You can checkout my [monokai](https://github.com/crusoexia/vim-monokai) scheme, use the 'dev' branch to check how it could works.

Thanks