Updated to highlight a few more language constructs in GitHub style

I updated the theme definition to cover a few more language constructs that GitHub was picking up differently from the theme. I tested mostly in PHP and Python, using Sublime Text 2. Most notably in PHP this pull request fixes constructs like 

```php
array()
isset()
array_merge()
```

In addition to all OOP style method invocation, such as 
```php
$this->getContent();
```
where the method name was not being highlighted correctly. In Python, errors like
```python
ImportError
```
should be handled correctly now as well. 

Let me know if there is anything I missed and I would be happy to send along another PR.