Public API v3 support

Removes Public API calls for v2 functions and implements v3. In addition, you can now enter a value in to the "limit" field to restrict how many output values you receive on calls to ```trades()``` and ```depth()```. Resolves tickets #4 and #10.<br>
Removes function:
* ```fee()```
Adds function: 
* ```info```<br><br>
Adds optional "limit" field to:
* ```trades()```
* ```depth()```