Supporting other tag types (beyond TODO and FIXME)

Would you be open to a PR which supports extracting other tag types (ie BUG, INFO, etc) 

Thinking it would be an idea to provide another options

```
// report on all types supplied
options.tagTypes = ['BUG','TODO','FIXME','INFO']

// use default items (backwards compatibility for TODO FIXME)
options.tagTypes = [];
```
