issue #308. 

Added an option not to append newline automatically when using a custom log formatter. 
Added this both to DDFileLogger and DDTTYLogger since there is no common superclass of just these 2. These change does not make sense for asl logger or any db loggers probably. 
The default value for this feature is to behave as previosly, so this should be backward compatible and not break any library clients that do not use this new behavior. 
We can swap first two conditions and remove second check of `isFormatter` (because it would be obvious, that in second case `isFormatter == YES`).

```
if (!isFormatted || _automaticallyAppendNewlineForCustomFormatters) {
    if (![logMsg hasSuffix:@"\n"]) {
        ...
    }
}
``` 

Everything else in this pull request looks good to me.