[4.1] Added better CA certificate bundle detection

Addresses issue #183.

This PR:

1. Allows you to define your own CA bundle.
2. Improves on the logic to detect a default CA certificate bundle to verify the peer.
3. Forces peer verification for every request for better security.
4. Removes the outdated CA bundle that was included in the repo. Now an exception is thrown if no CA bundle could be found.

Admittedly I'm not an expert on this matter. I just used the same logic as Guzzle on this one. So if there's an expert out there that can make this even better, speak now or forever hold your peace! :)