Making the gocardless client protected

Merge pull request #8 from hkwak/make-gocardless-protected

make gocardless property protected

add findSubscriptionsByCustomer method

Merge pull request #7 from hkwak/add-find-subscriptions-by-customer

introduce the FindSubscriptionsByCustomer method

Add findPaymentsBySubscription request

Merge pull request #6 from hkwak/add-find-payments-by-subscription-co…

…mmand

Add find payments by subscription command

Adding methods to Subscription Response

More work towards issue #5

Handle empty arrays in metadata fields

Minor bug fix

Add some methods to the Bank Account for returning data

Add some methods to the Bank Account for returning data

Outstanding function on PaymentResponse

New isOutstanding function says if they payment has processed yet.

Searchable Payments

Params from abstract now returns core values, search mechanism on payments via customer reference.

Error handling standardisation

Shift the error handling to the omnipay standard rather than throw exceptions.

Reenable PHP5 support

0.1.7

Fix day of month test failing due to lack of PHP7 support