Log objects directly.

I made patch to support logging Java objects and some primitives.
This patch enables users to log objects like these:

```java
logger.log("tag", "hello");
logger.log("tag", new Msg("hello", true));
```

outputs:
```
2013-09-03T01:06:35+00:00       myapp.tag  "hello"
2013-09-03T01:06:35+00:00       myapp.tag  {"message":"hello","valid":true"}
```

I also leave log(String, Map<String, Object>) method available.


regards.