Version 1.2

What's new:

• New functionality for invoice status management:
  • created helper class FakturowniaInvoiceStatus and added a new function changeInvoiceStatus() for Fakturownia class
  • added new variable pricePaid for FakturowniaInvoice class which automatically helps to change and manage invoice status
• Moved some of the classes to the new "Helper" namespace
• Updated Documentation for the current version