Add more example scripts

[OGKevin]

This issue is meant to keep track of the example scripts included in the SDK.

• [x] ApiContext
  • [x] Save/restore
  • [ ] Ensure that session is active
• [x] Attachments
• [ ] Callbacks
• [ ] Cards
  • [x] Order card
• [ ] Card payments
  • [ ] MasterCard action
• [ ] Cash registers
• [ ] Chat
• [ ] Connects
• [x] Export statements
• [ ] Invoices
• [ ] Monetary accounts
• [ ] Payment
  • [ ] Draft Payment
  • [ ] Scheduled Payment
  • [x] Payment batch
  • [x] Tab Payment
• [x] Request for payment / Request inquiry

• [x] User

  • bunq/sdk_php#98