Added option for maximum level in logLevelFilter

Added the ability to configure what maximum level will match the filter. Now you can filter a range of levels instead of allowing all that are above a threshold. 

**Usage**:
Add the `maxLevel` option in `logLevelFilter`, e.g.
```javascript
"appenders": [{
  "type": "logLevelFilter",
  "level": "DEBUG",
  "maxLevel": "INFO",
  "appender": {
    "type": "file",
    "filename": "debug_info.log"
  }
}]
```