cleaned up and made the callback example a little bit more verbose and clear
adjusted client_login example. added buy and account link, useing workaround for arg seperator and autologin on 400 error.
fixed a typo in paylink example
updated version to 2.3 for current changes, added changes to changelog, updated composer.json with relevant info
fixed config and tests for ClientTest where it was set up to go against production and checking the wrong config.
updated version identification in the client to 2.3