Allow removal or addition of newlines after blocks.

I'd like to use uncrustify for Objective-C but it's not fully configurable for my needs, especially when it comes to blocks.

I took a stab at trying to add a new rule: to allow `nl_after_brace_close` to be true while still nesting blocks inside messages like so:

```
[self.sendMessage withBlock:^{
    .....
}];
```
instead of

```
[self.sendMessage withBlock:^{
    .....
}
];
```

I'm not sure if this change fits into the larger scheme of things; this is the result of my investigating how to add new rules, so please send any feedback my way.