API methods now return the resulting response received from `perform_request`

Before, calling a method like `get_api_config` consisted of the following:

```
s.get_api_config()
config = s.response
print config
```

Now, you can simply:

```
config = s.get_api_config()
print config
```

This has been changed for all api methods for which is makes sense to do so.
Update README.md