Added BillingAddress state.
Added handlers for PaymentProcessor::HANDLER_CATCH_EXCEPTION.
Changed handlers arguments order.
Fixed examples.

Changed PaymentProcessor creation.
Added handlers for queries, that use executeQuery.
Added BillingAddress state.
Added handler for HANDLER_CATCH_EXCEPTION.
Added documentation for PaymentProcessor::setHandlers().
Fixed simple handlers.
Added article about Merchant callbacks.
Improved articles about payment scenarious.
Fixed links to methods source code.