These are the module writer's notes for v3.  See the regular
"notes_for_module_writers" file first.
- If your gateway is HTTPS-based, use (or convert to)
  Business::OnlinePayment::HTTPS !!
- Handling failures:
    - If your processor module encounters a setup problem, communication
      error or other problem that's prevents the card from even being
      run, you should die (or croak) with a useful error message.  Setting
      is_success to 0 and returning normally should only be done when the
      transaction *processing* was sucessful (or at least elicited some sort
      of result from the gateway), but the transaction itself returned a
      "normal" decline status of some sort.
       
    - (NEW IN 3.00_04) You should set "failure_status" depending on the
      specific failure result, if (and only if) the failure results from one
      of the defined statuses:
      - "expired"
      - "nsf" (non-sufficient funds / credit limit)
      - "stolen"
      - "pickup"
      - "blacklisted"
      - "inactive" (inactive card or not authorized for card-not-present) (?)
      - "decline" (other card/transaction declines only, not other errors)
   
      You should use code like this so your module can work with B:OP versions
      before 3.00_04:
        $self->build_subs('failure_status') unless $self->can('failure_status');
      (or add "failure_status" to your build_subs call if you have one during
      initialization)
- (NEW IN 3.01) Introspection:
  - Add an _info subroutine to your module that returns a hashref of
    information:
      sub _info {
        {
          'info_compat'           => '0.01', # always 0.01 for now,
                                             # 0.02 will have requirements
          'gateway_name'          => 'Example Gateway',
          'gateway_url'           => 'http://www.example.com/',
          'module_version'        => $VERSION,
          'supported_types'       => [ qw( CC ECHECK ) ],
          'token_support'         => 0, #card storage/tokenization support
          'test_transaction'      => 0, #set true if ->test_transaction(1) works
          'supported_actions'     => [
                                       'Normal Authorization',
                                       'Authorization Only',
                                       'Post Authorization',
                                       'Void',
                                       'Credit',
                                     ],
        };
      }
    # or a more complicated case:
      sub _info {
        {
          'info_compat'           => '0.01', # always 0.01 for now,
                                             # 0.02 will have requirements
          'gateway_name'          => 'Example Gateway',
          'gateway_url'           => 'http://www.example.com/',
          'module_version'        => $VERSION,
          'module_notes'          => 'usage notes',
          'supported_types'       => [ qw( CC ECHECK ) ],
          'token_support'         => 1,
          'test_transaction'      => 1,
          'supported_actions'     => { 'CC' => [
                                         'Normal Authorization',
                                         'Authorization Only',
                                         'Post Authorization',
                                         'Void',
                                         'Credit',
                                         'Recurring Authorization',
                                         'Modify Recurring Authorization',
                                         'Cancel Recurring Authorization',
                                       ],
                                       'ECHECK' => [
                                         'Normal Authorization',
                                         'Void',
                                         'Credit',
                                       ],
                                     },
          'CC_void_requires_card' => 1,
          'ECHECK_void_requires_account' => 1, #routing_code, account_number, name 
        };
      }
- authorization and order_number (NEWLY DOCUMENTED IN 3.01):
  Gateways will return one or two values from Authorization Only and
  Normal Authorization transactions that must be submitted back with a
  Post Authorization, Void, or Credit transaction.
  If the gateway returns one value, return this as "authorization"
  If the gateway returns two values, return one as "authorization" and the
  other as "order_number".  Typically "authorization" is the more low-level
  value returned from the underlying processing network while "order_number"
  is a unique tranaction id generated by the gateway.