Vivocha 0.6.20

Hi!
I had to add some features to log4js at my work and I thought those could be of interest. I added:
* subcategories: this allows to set a level for a major category then specify other levels for sub-categories. For example:
  "levels": {
    "cat": "WARN",
    "cat.sub1": "TRACE",
    "cat.sub1.sub12": "WARN",
    "cat.sub3": "INFO"
  }
If not specified, a sub-category inherits the level of its parent. Given the example configuration above, a logger with category "cat.sub4" would have level "WARN", inherited from category "cat". The appenders  also accept sub-categories, they will log the category and all sub-categories specified at their configurations. So, it is possible to create a logger only for category "cat.sub1.sub12".
* a level property at the file appender: this allows to restrict the levels that the file appender logs independent of the level configurations of the categories.
* a MARK level: this level is always logged and does not represent an error. Useful to send period marks to the log.
* a compression property at the rolling file appender: this activates compression of the rolled files. Unfortunately I can't tell if it works on other platforms than UNIX.

Let me know if it's worth to merge them,

Thanks,
Luis