Improve initialization and versionning API

• NEW: Deprecated Payplug::setSecretKey function, use Payplug::init instead.
• NEW: API version should now be specified explicitly from module.
• NEW: Improve Payplug setSecretKey with init method.
• NEW: Excluded configuration API_VERSION versionning, it will be send from the apps nowadays.

PSD2 Compliance

• Major: Replace customer by shipping and billing to be compliant with PSD2.
• New: Add versionning with new API_VERSION parameter.

Deferred payments

• New: Add deferred payments.

Installment plans

• New: Add installment plans.

2.5.1

• Bugfix: Fix packagist bundle.

2.5.0

• NEW: Add Authentication class for method specific to login and account permissions
• NEW: Add a method to patch payment
• NEW: Add a method to delete cards
• Breaking change: Remove classes and methods specific to customer

2.4.0

• NEW: Support for __isset magic method in resources. This should bring Twig support.
  (Thanks oservieres)
• NEW: Add a method to specify custom User-Agent products.

V2.3.0

• NEW: Support for Customer/Cards. (see official documentation)

• NEW: Payment objects can now be aborted.

  $payment->abort();
  

• Breaking change: Drop data key in objects collections (e.g. list of payments/list of refunds):

  $payments = \Payplug\Payment::listPayments();
  // $payment = $payments['data'][0]; // BEFORE
  $payment = $payments[0]; // NEW BEHAVIOR
  
  $refunds = \Payplug\Refund::listRefunds($payment);
  // $refund = $refunds['data'][0]; // BEFORE
  $refund = $refunds[0]; // NEW BEHAVIOR
  

• Breaking change: Drop deprecated classes PayPlugException and PayPlugServerException (with two uppercase
  letters in PayPlug). If you use **P__ayplugException and **P__ayplugServerException classes (with one
  uppercase letter in Payplug), you have nothing to do.

• NEW: This library is now under MIT Licence (Issue #4).

2.2.1: Merge pull request #3 from nilleroux/allow-tlsv10

Do not check OpenSSL version since TLS v1.0 is supported.