Add support for Trello "cardDueSoon" notification

Fixes issue #19. 

Looks like this:

```objectivec
    idMemberCreator = 4f0f14b38ed5f4e630019e7d;
    memberCreator =     {
        avatarHash = dc47ee8caec533c3b4319a1fe95924fc;
        fullName = "Walter White";
        id = 4f0f14b38ed5f4e630019e7d;
        initials = WW;
        username = walt;
    };
```