capitalize -> titleize, add capitalize and toSentence

Hey guys, this includes a few updates to helpers:

- rename `Batman.helpers.capitalize` -> `Batman.helpers.titleize` to be like Ruby/Rails helpers
- add `Batman.helpers.capitalize` and specs and docs
- add `Batman.helpers.toSentence` and specs and docs

I know this might not get accepted since some people might be using `capitalize` as `titleize` but of course, the fix is easy:

```
Batman.helpers.capitalize = Batman.helpers.titleize
```

Anyways, your call! Let me know if I can clean up these changes or anything.