Marker as a json

Adding option to log marker in a one level json format

Adding support for json parsing

In case the logs contain many custom fields and some of the custom fields have dynamic values. for example, a custom field called userName which contains the user that triggered a method.
In order to deal with this kind of custom fields, the logs are in a JSON format and the appender handles the parsing.

Gzip addition

Merge pull request #47 from logzio/sonatypeserver

Sonatypeserver