Added jsdoc for findElement and protractor.By

I've recently started using this excellent library and found I was manually editing the protractor files to add a little bit more jsdoc in order to make it easier to discover what it could do. This adds just a few bits of jsdoc to achieve the following:

## protractor.By

Before:
![image](https://f.cloud.github.com/assets/1056441/906754/2a1569cc-fcd6-11e2-86c0-11387e9a4969.png)

After:
![image](https://f.cloud.github.com/assets/1056441/906758/f80828f6-fcd6-11e2-8acf-e08d0a9ead80.png)

Note how it shows options from both the webdriver By and protractor-specific functions.

## ptor.findElement

Before:
![image](https://f.cloud.github.com/assets/1056441/906761/47e9ed1e-fcd7-11e2-9a52-ec5212d5e4ce.png)

After:
![image](https://f.cloud.github.com/assets/1056441/906764/b7b9fb52-fcd7-11e2-8102-d877eb87415a.png)

## ptor.findElements

Before:
![image](https://f.cloud.github.com/assets/1056441/906766/4a67a940-fcd8-11e2-9bf7-7a0a3855c83d.png)

After:
![image](https://f.cloud.github.com/assets/1056441/906777/37bf52c8-fcda-11e2-9f9f-dae26df068aa.png)

Not so useful as all you know is that you are getting a promise back.