Integration Tests now use -Dtests.config=/path/to/elasticsearch.yml

Add tests documentation
Fix IT test for #50
Update to Twitter4J 4.0.2

Closes #61.
Add note regarding User Stream integration test
Generate default mapping even if index already exists

If you create in advance your own index:

```
PUT /myindex
```

When the river starts, it does not add the default mapping.

Closes #62.
Support geo location array format

Closes #51.