Add ability to search for selected text in addition to whole words

I maintain / read a lot of module code, so I'm need to do a lot of API referencing inside custom modules. I run into a lot of functions formatted like this: 

```
function foo_bar_token_info() {
    // function contents
}
```

Using GoToDrupalApi on the previous function name (with or without a selection) currently searches for the entire word and resolves to ``http://api.drupal.org/api/drupal/7/search/foo_bar_page_tokens``  with 0 api results. 

My commit allows one to select just the ``token_info`` part of the name, and search for just the selection; if no selection is made, it defaults back to using the whole word.

Let me know if i've missed something, or if there is a coding style concern. Thanks!