Add support for {harmony: true} to react-tools

```
require('react-tools').transform(code, {harmony: true});
```

now enables all the harmony es6 transforms that are supported.

This is modeled after https://github.com/facebook/react/blob/master/bin/jsx#L17-L23
Merge pull request #1262 from vjeux/harmony-react-to

Add support for {harmony: true} to react-tools