Iterator added to Parser
Changes:
- Add a unit test for non-existent files when using VCardParser::parseFromFile() (throws an exception)
- Add a new method getCards(), which gets all cards. This is to complement the getCardAtIndex() method (which is great, but not sufficient).
- Implement the Iterator interface to loop over parsed data. Let me detail this last one.
PR #67, thanks to @wadmiraal