New functionality for performing post requests and getting raw response body

Hi,

I implemented two new methods with the following purposes:

1. post -> Allows a user to perform a simple HTTP Post request. This is very useful for testing APIs

2. getResponseBody -> A method that allows the user to fetch the raw response body. We use this for analyzing JSON responses

What to you think? I could also request a pull for the Driver Interface, but before that I wanted to make sure that you like the idea of having this new methods. Afterwards I could also integrate those methods into the other drivers before working on the interface.

Regards!