This line within `injectFile` wasn't doing much of anything:
```js
let expression = fs.readFile(filePath, 'utf8', (err, data) => callback({err, data}));
```
* That's fixed.
* A path error in examples/features.js is fixed.
* Test added for injectFile.
Certain examples rely extensively on the originating PhantomJS
examples.
This patch fixes license headers of these examples to mention
PhantomJS authors.
